52 Which of the prophets did your fathers not persecute? And they killed those who announced beforehand the coming of the Righteous One, whom you have now betrayed and murdered, 53 you who received the law as delivered by angels and did not keep it." - Acts 7:52-53
19 Why then the law? It was added because of transgressions, until the offspring should come to whom the promise had been made, and it was put in place through angels by an intermediary. 20 Now an intermediary implies more than one, but God is one. - Galatians 3:19-20
The New Testament authors seem to have a belief that the law of Moses was given through angels, but I am looking to find an Old Testament passage, preferably in the Pentateuch where the Law was delivered, that demonstrates or explains the role of angels in the revelation of the Law.