Is the sensation of something descending after urination, sometimes accompanied by the smell of urine and sometimes not, considered a form of waswasah (insinuating thoughts), and how can one ascertain the nature of this discharge?

A Muslim must do what he presumes will cut off the flow of urine. For a man, this involves "salt and natr" (massaging the perineum and pulling the penis), and for a woman, it involves "salt al-'ana" (massaging the pubic area). One should not pay attention to whispers of any remaining discharge. If a person doubts the exit of a drop after performing istibra' (cleansing after urination), it is excused. It is recommended to sprinkle water on the private parts and clothes after istinja' (washing after defecation or urination) to remove obsessive thoughts. There is no need to investigate or search for any sensation of discharge, but if one is certain of the presence of urine after investigation, then the wudu' is invalidated, and the clothes become impure.