How can one deal with drops of urine coming out after using water for cleansing (istinja'), and what is the ruling on washing underwear in this situation?

It is obligatory to be careful by placing a tissue or similar item on the organ to prevent the impurity from spreading to the clothes. Then, perform istinja' (washing after relieving oneself), wudu' (ablution), and prayer after the discharge of impurity ceases. If this is not done, then according to the majority of scholars, it is obligatory to pour water on the part of the clothes that has become impure. The Malikis, however, view this impurity as excusable as long as it recurs daily. Adopting the view of the majority is more cautious, but it is permissible for common people to follow the Maliki school when there is a need. In no case is it permissible to delay the prayer beyond its prescribed time.