Musnad Ahmad 329:21

Sufyan narrated to us, from al-Zuhri, from 'Abbad ibn Tamim, from his uncle, that he complained to the Messenger of Allah (peace and blessings of Allah be upon him) about a man who finds something during prayer, and it is imagined to him that something has occurred from him. He said: "He should not turn away [from the prayer] until he finds a scent or hears a sound."