It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him and his family) led them in prayer and he (peace and blessings be upon him and his family) forgot. Then when he (peace and blessings be upon him and his family) finished the prayer with salam, he performed two prostrations and then finished with salam again.