Musnad Ahmad 31:906

'Affan narrated to us, Hammad bin Salamah narrated to us, from 'Ali bin Zayd, from Sa'id bin al-Musayyib, from Abu Sa'id al-Khudri, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The servant remains in prayer as long as he is in his place of prayer, waiting for the prayer. The angels say: 'O Allah, forgive him; O Allah, have mercy on him,' until he leaves or breaks his wudu (hadath)." I said: "What is 'hadath'?" He said: "Like this." I said to Abu Sa'id, and he said: "Passing wind silently or audibly."