He [Al-Khiraqi] said: Ritual cleansing [istinjaa] is not required of anyone who falls asleep or passes gas.
We know of no disagreement regarding this. Abu Abdullah said: Istinjaa is not made obligatory in the case of gas, neither in the book of Allah nor in the sunnah of His Prophet, but ablution [wudu’] does become obligatory. It is narrated from the Prophet (SAW) that He said: Anyone who performs istinjaa after passing gas is not one of us. (Narrated by Al-Tabarani in Al-mu’jam Al-saghir].