Musnad Ahmad 30:774

Ibrahim ibn Khalid narrated to us, Abd al-Rahman ibn Budhawaih informed me, he informed me of one who heard Wahb saying: He informed me—meaning Hammam—(Abdullah ibn Ahmad said: Thus my father said), Abu Hurairah said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "One of you remains in prayer as long as he is waiting for the one that follows it, and the angels continue to pray for one of you as long as he remains in his place of prayer, saying: 'O Allah, forgive him; O Allah, have mercy upon him,' as long as he does not commit a *hadath* (ritual impurity)." He said: A man from the people of Hadramawt said: "And what is that *hadath*, O Abu Hurairah?" He said: "Allah is not ashamed of the truth: it is if he passes wind silently or audibly."