Abbad bin Tamim narrates from his paternal uncle Abdullah bin Zayd (may Allah be pleased with him) that a man complained to him (peace and blessings be upon him) that he felt some doubt in his prayer: what should he do? He (peace and blessings be upon him) said: "He should not break off his prayer until he hears a sound or notices a smell."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3374