Only two real candidates exist, those being Psalm 97:7, and Deuteronomy 32:43.
Psalm 97:6-9 (DRB)
The heavens declared his justice: and all people saw his glory. 7 Let them be all confounded that adore graven things, and that glory in their idols. Adore him, all you his angels: 8 Sion heard, and was glad. And the daughters of Juda rejoiced, because of thy judgments, O Lord. 9 For thou art the most high Lord over all the earth: thou art exalted exceedingly above all gods.
Deuteronomy 32:43 (DRB)
Praise his people, ye nations, for he will revenge the blood of his servants: and will render vengeance to their enemies, and he will be merciful to the land of his people.
You might wonder what this latter has to do with our passage in Hebrews. Well, there exists textual traditions supporting the idea that this passage originally read: "Rejoice with him, O heavens, and adore him, all ye angels."
A manuscript called 4QDeut32 from the Qumran scrolls reads as follows:
...הדנינו שמים עמו
והשתחוו לו כל אלהים...
...Rejoice with him, O heavens,
And adore him, all ye angels (or "And let all the angels adore him")...
Indeed, the Septuagint has also (cf. Justin Martyr, Dialogue, 130, circa A.D. 155):
εὐφράνθητε οὐρανοί ἅμα αὐτῷ
καὶ προσκυνησάτωσαν αὐτῷ πάντες υἱοὶ θεοῦ
Rejoice with him, O heavens,
And let all the sons of God adore him.
The Septuagint, it has been suggested, in various places gingerly translates passages open to misinterpretation by a secular or Greek audience (the tradition is, after all, that it was translated for secular Greeks, more or less under duress). If this is the case here, then "sons of God" as a translation of "elohim" more than makes sense, since it tips people off partially to the original Hebrew who speak Hebrew ("elohim") and was understood to refer to angels regardless, which as a tradeoff of carefulness and faithfulness in translation, is definitely a success.
It would appear that the author of Hebrews is citing a Greek translation, which most probably read "sons of God" but which was of course understood to refer to nothing other than the angels, and so he makes it explicit for the sake of brevity and cutting to the chase, since such would be an interpretation of little consequence, and by no means controversial.
In any case, the source text would be conflating "the heavens" with its inhabitants, i.e. the angels (although one might note that in Job 38:7 "sons of God" arguably means "stars," as opposed to "the angels.") It amounts, after all, to the difference between "the angels" and "the angels θεου (of God)" given the Hebrew, and no one would have any quibble about adding "of God" to "the angels."
As for the point of the author of Hebrews, he is adducing Scriptural passages which are markedly aimed at a divine person, not a creature, in order to show that Jesus is far above angels. Perhaps evidence against understanding this to be a quotation of Deuteronomy, and instead of Psalm 97 would be the almost beyond coincidence proximity of the phrase "For thou art the most high Lord over all the earth: thou art exalted exceedingly above all elohim," which would be in the minds of his readers as those who know the Scriptures, and they would understand that he refereed to that text for that reason (i.e. elohim is the same word in the phrase "Adore him, all elohim" and in "[he is] exalted exceedingly above all elohim"), which would nicely prove in one fell sweep the author's point that Jesus is adore by angels, yet exalted high above them. One argument against this is the prefixed "And" (as in "And let..."). This does not fit the context of Hebrews, but must be quoation; except in Psalm 97, there is no "and." Whereas there is and "And" in Deuteronomy.
Another possibility is that he is blending several scriptures into one scripture-thought or doctrine taught by several passages.
Take for example:
Psalm 103:20 (DRB) Bless the Lord, all ye his angels: you that are mighty in strength, and execute his word, hearkening to the voice of his orders. 21 Bless the Lord, all ye his hosts: you ministers of his that do his will.
Quoting those other texts, would bring to mind the subservience of angels, and that they are "all ministering spirits, sent to minister for them, who shall receive the inheritance of salvation."
Speaking of which: what do we read 5 verses after the above quotation?
Psalm 104:4 (DRB) Who makest thy angels spirits: and thy ministers a burning fire.
In fact, this cluster of quotations all seem to refer to one portion of the Psalms taken as some kind of unit (and which read like one Psalm).
Hebrews 1:6-14 (DRB) And again, when he bringeth in the first begotten into the world, he saith: And let all the angels of God adore him. 7 And to the angels indeed he saith: He that maketh his angels spirits, and his ministers a flame of fire. 8 But to the Son: Thy throne, O God, is for ever and ever: a sceptre of justice is the sceptre of thy kingdom. 9 Thou hast loved justice, and hated iniquity: therefore God, thy God, hath anointed thee with the oil of gladness above thy fellows. 10 And: Thou in the beginning, O Lord, didst found the earth: and the works of thy hands are the heavens. 11 They shall perish, but thou shalt continue: and they shall all grow old as a garment. 12 And as a vesture shalt thou change them, and they shall be changed: but thou art the selfsame, and thy years shall not fail. 13 But to which of the angels said he at any time: Sit on my right hand, until I make thy enemies thy footstool? 14 Are they not all ministering spirits, sent to minister for them, who shall receive the inheritance of salvation?
Psalm 102 - Psalm 104:1-4 (DRB)
1 The prayer of the poor man, when he was anxious, and poured out his supplication before the Lord. 2 HEAR, O Lord, my prayer: and let my cry come to thee. 3 Turn not away thy face from me: in the day when I am in trouble, incline thy ear to me. In what day soever I shall call upon thee, hear me speedily. 4 For my days are vanished like smoke: and my bones are grown dry like fuel for the fire. 5 I am smitten as grass, and my heart is withered: because I forgot to eat my bread. 6 Through the voice of my groaning, my bone hath cleaved to my flesh. 7 I am become like to a pelican of the wilderness: I am like a night raven in the house. 8 I have watched, and am become as a sparrow all alone on the housetop. 9 All the day long my enemies reproached me: and they that praised me did swear against me. 10 For I did eat ashes like bread, and mingled my drink with weeping. 11 Because of thy anger and indignation: for having lifted me up thou hast thrown me down. 12 My days have declined like a shadow, and I am withered like grass. 13 But thou, O Lord, endurest for ever: and thy memorial to all generations. 14 Thou shalt arise and have mercy on Sion: for it is time to have mercy on it, for the time is come. 15 For the stones thereof have pleased thy servants: and they shall have pity on the earth thereof. 16 And the Gentiles shall fear thy name, O Lord, and all the kings of the earth thy glory. 17 For the Lord hath built up Sion: and he shall be seen in his glory. 18 He hath had regard to the prayer of the humble: and he hath not despised their petition. 19 Let these things be written unto another generation: and the people that shall be created shall praise the Lord: 20 Because he hath looked forth from his high sanctuary: from heaven the Lord hath looked upon the earth. 21 That he might hear the groans of them that are in fetters: that he might release the children of the slain: 22 That they may declare the name of the Lord in Sion: and his praise in Jerusalem; 23 When the people assemble together, and kings, to serve the Lord. 24 He answered him in the way of his strength: Declare unto me the fewness of my days. 25 Call me not away in the midst of my days: thy years are unto generation and generation. 26 In the beginning, O Lord, thou foundedst the earth: and the heavens are the works of thy hands. 27 They shall perish but thou remainest: and all of them shall grow old like a garment: And as a vesture thou shalt change them, and they shall be changed. 28 But thou art always the selfsame, and thy years shall not fail. 29 The children of thy servants shall continue: and their seed shall be directed for ever.
1 For David himself. BLESS the Lord, O my soul: and let all that is within me bless his holy name. 2 Bless the Lord, O my soul, and never forget all he hath done for thee. 3 Who forgiveth all thy iniquities: who healeth all thy diseases. 4 Who redeemeth thy life from destruction: who crowneth thee with mercy and compassion. 5 Who satisfieth thy desire with good things: thy youth shall be renewed like the eagle's. 6 The Lord doth mercies, and judgment for all that suffer wrong. 7 He hath made his ways known to Moses: his wills to the children of Israel. 8 The Lord is compassionate and merciful: longsuffering and plenteous in mercy. 9 He will not always be angry: nor will he threaten for ever. 10 He hath not dealt with us according to our sins: nor rewarded us according to our iniquities. 11 For according to the height of the heaven above the earth: he hath strengthened his mercy towards them that fear him. 12 As far as the east is from the west, so far hath he removed our iniquities from us. 13 As a father hath compassion on his children, so hath the Lord compassion on them that fear him: 14 for he knoweth our frame. He remembereth that we are dust: 15 man's days are as grass, as the flower of the field so shall he flourish. 16 For the spirit shall pass in him, and he shall not be: and he shall know his place no more. 17 But the mercy of the Lord is from eternity and unto eternity upon them that fear him: And his justice unto children's children, 18 to such as keep his covenant, And are mindful of his commandments to do them. 19 The Lord hath prepared his throne in heaven: and his kingdom shall rule over all. 20 Bless the Lord, all ye his angels: you that are mighty in strength, and execute his word, hearkening to the voice of his orders. 21 Bless the Lord, all ye his hosts: you ministers of his that do his will. 22 Bless the Lord, all his works: in every place of his dominion, O my soul, bless thou the Lord.
1 For David himself. BLESS the Lord, O my soul: O Lord my God, thou art exceedingly great. Thou hast put on praise and beauty: 2 and art clothed with light as with a garment. Who stretchest out the heaven like a pavilion: 3 who coverest the higher rooms thereof with water. Who makest the clouds thy chariot: who walkest upon the wings of the winds. 4 Who makest thy angels spirits: and thy ministers a burning fire. 5 Who hast founded the earth upon its own bases: it shall not be moved for ever and ever. 6 The deep like a garment is its clothing: above the mountains shall the waters stand. 7 At thy rebuke they shall flee: at the voice of thy thunder they shall fear. 8 The mountains ascend, and the plains descend into the place which thou hast founded for them. 9 Thou hast set a bound which they shall not pass over; neither shall they return to cover the earth. 10 Thou sendest forth springs in the vales: between the midst of the hills the waters shall pass. 11 All the beasts of the field shall drink: the wild asses shall expect in their thirst. 12 Over them the birds of the air shall dwell: from the midst of the rocks they shall give forth their voices. 13 Thou waterest the hills from thy upper rooms: the earth shall be filled with the fruit of thy works: 14 Bringing forth grass for cattle, and herb for the service of men. That thou mayst bring bread out of the earth: 15 and that wine may cheer the heart of man. That he may make the face cheerful with oil: and that bread may strengthen man's heart. 16 The trees of the field shall be filled, and the cedars of Libanus which he hath planted: 17 there the sparrows shall make their nests. The highest of them is the house of the heron. 18 The high hills are a refuge for the harts, the rock for the irchins. 19 He hath made the moon for seasons: the sun knoweth his going down. 20 Thou hast appointed darkness, and it is night: in it shall all the beasts of the woods go about: 21 The young lions roaring after their prey, and seeking their meat from God. 22 The sun ariseth, and they are gathered together: and they shall lie down in their dens. 23 Man shall go forth to his work, and to his labour until the evening. 24 How great are thy works, O Lord? thou hast made all things in wisdom: the earth is filled with thy riches. 25 So is this great sea, which stretcheth wide its arms: there are creeping things without number: Creatures little and great. 26 There the ships shall go. This sea dragon which thou hast formed to play therein. 27 All expect of thee that thou give them food in season. 28 What thou givest to them they shall gather up: when thou openest thy hand, they shall all be filled with good. 29 But if thou turnest away thy face, they shall be troubled: thou shalt take away their breath, and they shall fail, and shall return to their dust. 30 Thou shalt send forth thy spirit, and they shall be created: and thou shalt renew the face of the earth. 31 May the glory of the Lord endure for ever: the Lord shall rejoice in his works. 32 He looketh upon the earth, and maketh it tremble: he toucheth the mountains, and they smoke. 33 I will sing to the Lord as long as I live: I will sing praise to my God while I have my being. 34 Let my speech be acceptable to him: but I will take delight in the Lord. 35 Let sinners be consumed out of the earth, and the unjust, so that they be no more: O my soul, bless thou the Lord.
It says, "when he bringeth his firstborn into the world," so "let all the angels worship him" refer to the incarnate Son, not to some later event after his birth, or at His second coming.