Musnad Ahmad 31:911

'Affan narrated to us, Hammad ibn Salamah narrated to us, from 'Ali ibn Zayd, 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 devil 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 wind. So, he must not depart until he hears a sound or finds a smell."