Ablution

1.
Narrated Abu Huraira:
Allah's Apostle said, "The prayer of a person who does ,Hadath (passes, urine, stool or wind) is not accepted till he performs (repeats) the ablution." A person from Hadaramout asked Abu Huraira, "What is 'Hadath'?" Abu Huraira replied, " 'Hadath' means the passing of wind from the anus."
(Bukhari)

2.
Narrated 'Abbas bin Tamim:
My uncle asked Allah's Apostle about a person who imagined to have passed wind during the prayer. Allah' Apostle replied: "He should not leave his prayers unless he hears sound or smells something."
(Bukhari)