The problem occurs in v. 10 as well, where variant readings between "Amos" and "Amon" occur. That is, like "Asaph" and "Asa," the words are near homonyms with the respective psalmist Asaph and prophet Amos. In this regard, the late Bruce Metzger (1994) comments as follows on these verses:
1:7–8 Ἀσάφ, Ἀσάφ {B}
It is clear that the name “Asaph” is the earliest form of text preserved in the manuscripts, for the agreement of Alexandrian (א B) and other witnesses (f 1 f 13 700 1071) with Eastern versions (cop arm eth geo) and representatives of the Western text (Old Latin mss and D in Luke [D is lacking for this part of Matthew]) makes a strong combination. Furthermore, the tendency of scribes, observing that the name of the psalmist Asaph (cf. the titles of Pss 50 and 73 to 83) was confused with that of Asa the king of Judah (1 Kgs 15:9 ff.), would have been to correct the error, thus accounting for the prevalence of Ἀσά in the later Ecclesiastical text and its inclusion in the Textus Receptus. In the genealogy in 1 Chr 3:10 most Greek manuscripts read Ἀσά, though ms. 60 reads Ἀσάβ. In Antiq. VIII.xi.3–xii.6 Josephus uses Ἄσανος, though in the Latin translation Asaph appears.
Although most scholars are impressed by the overwhelming weight of textual evidence supporting Ἀσάφ, Lagrange demurs and in his commentary prints Ἀσά as the text of Matthew. He declares (p. 5) that “literary criticism is not able to admit that the author, who could not have drawn up this list without consulting the Old Testament, would have taken the name of a psalmist in place of a king of Judah. It is necessary, therefore, to suppose that Ἀσάφ is a very ancient [scribal] error.” Since, however, the evangelist may have derived material for the genealogy, not from the Old Testament directly, but from subsequent genealogical lists, in which the erroneous spelling occurred, the Committee saw no reason to adopt what appears to be a scribal emendation in the text of Matthew.
1:10 Ἀμώς, Ἀμώς {B}
The textual evidence for the reading “Amos,” an error for “Amon,” the name of the king of Judah, is nearly the same as that which reads Ἀσάφ in verses 7 and 8.
In 1 Chr 3:14 most manuscripts present the correct Ἀμών (or its near equivalent Ἀμμών), but Ἀμώς is read by A B (B* and one minuscule read Ἀμνών). In the narrative account concerning King Amon in 2 Kgs 21:18–19, 23–25; 2 Chr 33:20–25 several Greek witnesses erroneously read Ἀμώς.
Despite Lagrange’s preference for Ἀμών (see his argument quoted above on verses 7–8), the Committee was impressed by the weight of the external evidence that attests Ἀμώς.
In summary, the Committee did not ascribe their highest confidence rating {A} to the received reading because the Codex Washingtonianus (c. 400) attests to the "correct" reading, but is at odds with other manuscripts (dated at the same time) with the "incorrect" readings (such as א B C, etc.). In other words, there exists doubt (or possibility) that the "Vorlage" of the the Codex Washingtonianus was some manuscript reflecting the "correct" reading as found in most manuscripts of the Greek Septuagint (in reference to 1 Chr 3:10,14), which reads Ἀσά and Ἀμών, respectively: this "correct" reading appears to have carried into the the Codex Washingtonianus. To put it another way, the "incorrect" readings were not extant at the time of the First Century in most manuscripts of the Greek Septuagint, but sometime between the First Century and the Fourth Century, the variant "incorrect" readings of Ἀσάφ and Ἀμώς began to appear in the earliest manuscripts of the Greek New Testament (with the sole exception of the Codex Washingtonianus).
REFERENCE:
Metzger, Bruce M. (1994). A Textual Commentary on the Greek New Testament (4th rev. ed.). London; New York: United Bible Societies, 1-2.
