Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: "Satan comes to one of you during his prayer and takes hold of a hair at his rear, so that he thinks his ablution has been broken. So let him not turn away from the prayer until he hears a sound or perceives a smell."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9198