Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) says: The Prophet (peace and blessings be upon him) did not fight in a sacred month, except when war was imposed on him or people fought (then he would face them). When such a situation arose (while a sacred month was in progress), he would stay put until it had passed.
Ahmad recorded it, and its narrators are the narrators of the Sahih.