We are not told about the content of the church’s prayer. Since they are surprised by Peter’s release (Acts 12:14–17), it is likely that they were praying for a positive outcome from the trial, a lesser punishment or Peter’s well-being/bold witness in general.1
5 Pierre donc était gardé dans la prison; et l'Eglise ne cessait d'adresser pour lui des prières à Dieu.