Acts 12:3-7

When he saw that it pleased the Jews, he proceeded to arrest Peter as well. (Now these were the days of Unleavened Bread.)

When he had arrested him, he put him in prison, turning him over to four squads of soldiers to guard him, intending only after the Passover to bring him before the people.

So Peter was kept in the prison, but prayer for him was being made to God intensely by the church.

On the very night when Herod was about to bring him forward, Peter was sleeping between two soldiers, bound with two chains, and guards in front of the door were watching over the prison.

And behold, an angel of the Lord suddenly stood near Peter, and a light shone in the cell; and he struck Peter’s side and woke him, saying, “Get up quickly.” And his chains fell off his hands.