Acts 12:4-6

When he had seized Peter, he put him in prison, turning him over to four squads of soldiers of four each to guard him [in rotation throughout the night], planning after the Passover to bring him out before the people [for execution]. So Peter was kept in prison, but fervent and persistent prayer for him was being made to God by the church. The very night before Herod was to bring him forward, Peter was sleeping between two soldiers, bound with two chains, and sentries were in front of the door guarding the prison.