The reading is from Acts of the Apostles 12:1-11

About that time, Herod the king laid violent hands upon some who belonged to the church. He killed James the brother of John with the sword; and when he saw that it pleased the Jews, he proceeded to arrest Peter also. This was during the days of Unleavened Bread. And when he had seized him, he put him in prison, and delivered him to four squads of soldiers to guard him, intending after the Passover to bring him out to the people. So Peter was kept in prison; but earnest prayer for him was made to God by the Church.

The very night when Herod was about to bring him out, Peter was sleeping between two soldiers, bound with two chains, and sentries before the door were guarding the prison; and behold, an angel of the Lord appeared, and a light shone in the cell; and he struck Peter on the side and woke him, saying, "Get up quickly." And the chains fell off his hands. And the angel said to him, "Wrap your mantle around you and follow me." And he went out and followed him; he did not know that what was done by the angel was real, but thought he was seeing a vision. When they had passed the first and the second guard, they came to the iron gate leading into the city. It opened to them of its own accord, and they went out and passed on through one street; and immediately the angel left him. And Peter came to himself, and said, "Now I am sure that the Lord has sent his angel and rescued me from the hand of Herod and from all that the Jewish people were expecting."