It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever imagines during his prayer that his ablution has been broken should not leave his prayer until he hears a sound or perceives a smell."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11898