What is the ruling on the presence of yellowish discharge with an unpleasant odor after performing istinja' (ablution after defecation) and ensuring purity, and is it obligatory to always check for it? What are the implications if it is found after prayer or in a place where performing istinja' is difficult, and how should one deal with it?

The obligation in Istinja' (cleansing after defecation or urination) is to be certain or to predominantly believe that purification has occurred. Once this is achieved, one's obligation is discharged, and there is no need to inspect the area. The default assumption is that nothing emerges after Istinja'. If something that necessitates Istinja' does emerge, Istinja' for it becomes immediately obligatory. If there is doubt about the time a impurity emerged, it should be attributed to the last possible time it could have emerged. If removing the impurity is difficult, its removal should be delayed until the time of prayer, then one should perform Istinja' and Wudu' (ablution), as avoiding impurity is a condition for the validity of prayer. If one is unable to remove it, one should pray in their current state. Feces are not among the excusable impurities, and wind (flatulence) does not have a substance that soils the area, so Istinja' is not obligatory for it.