Acts 12:7

Again an angel of the Lord (Gr. angelos kyriou) visited Peter in prison (Acts 5:19; cf. Acts 8:26; Acts 12:23). A light also illuminated his cell (cf. Acts 9:3). The angel instructed him to get up quickly, and when he did his chains fell from his hands. Peter’s guards slept through the whole event.

"Luke clearly regards Peter’s escape as a miracle, a divine intervention by a supernatural visitant (cf. Luke 2:9) . . ." [Note: Neil, p. 149.]

Thomas Watson, the Puritan preacher, reportedly said, "The angel fetched Peter out of prison, but it was prayer that fetched the angel." [Note: Wiersbe, 1:452-53.]