Praise be to Allaah.
What invalidates wudoo’ is wind that comes
out of the back passage. This is what invalidates wudoo’, because according to the hadeeth of ‘Abd-Allaah ibn Zayd, a man thought that he had
broken his wudoo’ whilst praying when he had not done so, and the Prophet (peace and blessings of Allaah be upon him) said: “Do not stop
praying until you hear a sound or smell an odour.” If something happens in his stomach and he is not sure whether he has broken his wudoo’ or not,
then the basic principle is that he is still pure (still has wudoo’).
Shaykh Dr Khaalid al-Mushayqih.