1. Everyday when I wake up from sleep I find one white stain on my underwear. Should I change my underwear and pants every day or is it pure? Even if it is Madi or wazi?

2. Once I woke up from sleep and really needed to use the bathroom, as soon as I undressed a drop of urine leaked to the floor. I often wake up in the state of really needing to use the bathroom. Should I always assume that urine leaked during my sleep and that my pants are impure?

1) They are Tahir.

2) If you are sure that whatever stain or wetness is there is from urine then it is najis. If you are not sure then it is not necessary to change.