Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: Satan circles around a man during his prayer in order to spoil his prayer for him. When the man wears him out, he blows into the man's rear (so that the man feels he may have broken his ablution). When any of you senses something like this, he should not end his prayer until he perceives a smell or hears a sound.
Al-Tabarani recorded it; its narrators have been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الطهارة / 1252