Abdullah bin Zayd (may Allah be pleased with him) says that a complaint was made to the Prophet (peace and blessings be upon him) about a man who imagines that he has felt something during prayer. He (peace and blessings be upon him) said: "He should not leave the prayer until he hears a sound or perceives a smell."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 15133