Acts 16:22-26

The crowd also joined in the attack against them, and the chief magistrates tore their robes off them and ordered that Paul and Silas be beaten with rods. [2 Cor 11:25] After striking them many times [with the rods], they threw them into prison, commanding the jailer to guard them securely. He, having received such a [strict] command, threw them into the inner prison (dungeon) and fastened their feet in the stocks [in an agonizing position]. But about midnight when Paul and Silas were praying and singing hymns of praise to God, and the prisoners were listening to them; suddenly there was a great earthquake, so [powerful] that the very foundations of the prison were shaken and at once all the doors were opened and everyone’s chains were unfastened.