Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.035A.

This would include urine, feces (Allah says, “…or one of you comes from relieving himself,” thus proving that such an act obligates a new purification), and releasing gas from the anus. Abu Hurairah reported that the Messenger of Allah said, “Allah does not accept the prayer of a person who has released gas until he makes a new ablution. A person from Hazhramaut asked Abu Hurairah, “What does releasing gas mean?” He answered, “Wind with or without sound.” (Related by al-Bukhari and Muslim.) He also narrated that the Prophet said, “If one of you finds a disturbance in his abdomen and is not certain if he has released any gas or not, he should not leave the mosque unless he hears its sound or smells its scent.” (Related by Muslim.)

Hearing the escaping gas or smelling it is not a condition for nullifying ablution, but he stressed that one should be certain of the action. As for al-Mazhi (prostatic fluid), the Prophet said, “Make ablution.” Concerning sperm or al-mani, said Ibn ‘Abbas “It requires ghusl and for al-mazhi and al-wadi, wash your sex organs and make ablution.” This was related by al-Baihaqi in his Sunan.