Is it obligatory for the fasting person to expel whatever is in their throat from belching or regurgitation, even if it has not reached the mouth, even if they intentionally belched and nothing from the regurgitation reached the mouth?

If the regurgitated matter (qals) is within the inner limits [of the throat] and has not gone past the pharynx, then it is not permissible to intentionally expel it. Whoever does so deliberately has invalidated their fast, because this is considered intentional vomiting (istiqā’ah), which is a fast-breaker according to the majority of scholars. So, whoever intentionally vomits must make up the fast, and this is the view of the general body of scholars. This applies whether the expelled vomit from intentional vomiting is little or much, as long as the fasting person intended to expel it.

However, if the regurgitated matter (qals) or vomit comes out involuntarily and reaches the outer limits [of the mouth], then one must spit it out. It is not permissible to intentionally swallow it; otherwise, the fast would be invalidated. If one spits it out and expels it, their fast is not invalidated.