Must I look at my underpants to ensure the exit of madhy when I feel my penis sticking to it, bearing in mind that I wash my penis and pour water on my underpants to repel whispers [of doubt] before prayer?

The person afflicted with waswas (obsessive doubts) must ignore these whispers and pay no attention to them. So, he should not wash his private parts before prayer unless he is certain that something has exited. If he performs istinja' (washing after defecation/urination) and verifies that an impurity has exited, he should not pay attention to doubt after washing, nor should he inspect his underwear. Rather, he should completely ignore these whispers.