Musnad Ahmad 31:912

'Affan narrated to us, Hammad ibn Salamah narrated to us, from 'Ali ibn Zayd, from Abu Nadrah, and from Sa'id ibn al-Musayyib, from Abu Sa'id al-Khudri, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, the Shaytan comes to one of you while he is in his prayer, and he takes a hair from his posterior and pulls it, so he thinks that he has broken his wudu (passed wind). So he should not depart until he hears a sound or finds a smell."