Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1162
Abu Huraira reported: The Messenger of Allah (may peace be upon him) said: The devil takes to his heels breaking wind when the prayer begins. and the rest is the same but with this addition:" He (the devil) makes him think of pleasant things (or things productive of enjoyment) and of the things wished for, and reminds him of such needs which he had forgotten."