Acts 12:1-5

Now at that time Herod [Agrippa I] the king [of the Jews] arrested some who belonged to the church, intending to harm them. And he had James the brother of John put to death with a sword; and when he saw that it pleased the Jews, he proceeded to have Peter arrested as well. This was during the days of Unleavened Bread [the Passover week]. 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.