Praise be to Allah.
The Messenger of Allah (peace and blessings of Allah be upon him) explained to us the guidelines concerning stopping praying in the case asked about here. It was narrated that Abu Hurayrah (may Allah be pleased with him) said: “The Messenger of Allah (peace and blessings of Allah be upon him) said: ‘If any one of you feels something in his stomach, and he is not sure whether anything came out of him or not, let him not leave the mosque unless he hears a sound or detects an odour.’” (Narrated by Muslim, 362)
It was narrated that ‘Abd-Allah ibn Zayd said: “The Prophet (peace and blessings of Allah be upon him) was told about a man who imagined that he felt something whilst he was praying. He said, ‘Let him not stop [praying] unless he hears a sound or detects an odour.’” (Agreed upon).
Imaam al-Nawawi said in Sharh Muslim, 4/49: this hadeeth forms one of the basic principles of Islam and an important principle of fiqh. Things are judged to remain as they are until there is certainty that a change has occurred, and having doubts does not alter the fact.
It is not considered to be najaasah until it emerges. Sounds may come from a person’s stomach as the result of food being moved (along the digestive tract). If the worshipper hears a sound inside his stomach but nothing comes out of him that would break his wudoo’, and he does not note anything that would indicate that, such as hearing a sound or smelling an odour, then he should not pay any attention to it, because the basic principle is that he remains taahir (pure). So his wudoo’ is not broken and he should not stop praying unless he is certain that something has come out of him, because what is certain is not overruled by what is doubtful.
And Allah knows best.