Does a person who donates clothes (pants and revealing blouses) sin if the needy wear them as they are, even though his intention was to gain reward?

It is impermissible to donate immodest clothing except to someone known not to disobey Allah with it in front of non-mahram men, while emphasizing to her and warning her against immodesty, because that which leads to haram is haram, and because means share the rulings of their ends. If no one can benefit from it in a permissible way, then do not donate it at all.