Praise be to Allah.
If a person is sure that he has passed wind, then he has to do wudoo’, but if it is simply the movement of gas in the stomach, or he imagines that he may have passed wind, then he should not pay any attention to it. The evidence that the mere movement of gas in the stomach or imagining that one may have passed wind does not invalidate wudoo’ is the hadeeth whose authenticity is agreed upon, narrated from ‘Abd-Allaah ibn Zayd, who said:
“The Prophet (peace and blessings of Allaah be upon him) was asked about a man who felt something during his prayer – should he stop praying? He said, ‘No, not unless you hear a sound or detect an odour.’” (Narrated by al-Bukhaari, 1915; Muslim, 540). Al-Nawawi said: this hadeeth sets out the principle that things should remain as they are unless one is certain that they have changed; doubt does not affect the status quo.
Ibn Hajar said: the majority of scholars followed this hadeeth.
Paying attention to these doubts may lead to one being affected by insinuating whispers of the Shaytaan (waswaas), so we must not pay attention to that, except in cases where wind is definitely passed. Then wudoo’ is required. Al-Nawawi said, concerning the phrase “unless you hear a sound or detect an odour”: “it is sufficient to know that one or the other is present; it is not a condition that both the sound and the odour be present, according to the consensus of the Muslims.” What is meant here by knowing is being certain. And Allaah knows best.