Is it permissible to retain gas during prayer when suffering from irritable bowel syndrome, and if odorless gas is expelled, is it obligatory to repeat ablution and prayer, and is it permissible to pray while sitting due to severe stomach pain?

The prayer is valid when holding back gas as long as nothing is emitted. It is disliked to proceed with prayer in this condition if it can be avoided. If the emission of gas stops for a time sufficient for ablution and prayer, then it is not considered سلس ( سلس is a continuous discharge from the body that is difficult to control like incontinence), and ablution is nullified by the emission of gas, even if it is a small amount. However, if the emission of gas is continuous, it falls under the ruling of سلس, and one must perform ablution for each prayer after its time has begun, while taking precautions as much as possible, and what is emitted does not matter. Standing is a pillar of prayer, so sitting is not sufficient if one is able to stand. Prayers performed sitting while one was able to stand must be repeated. However, if the pain is severe, such that standing would cause extreme hardship, then it is permissible to pray sitting.