Does semen that has stained a blanket transfer to clothing if the impurity has dried and not been washed, and is prayer with such clothing acceptable?

The preponderant opinion is that semen is pure, and things it gets on do not require purification. Rather, it is only recommended to wash it off and remove it. Therefore, prayer performed on a spot or in a garment that has been touched by semen is valid, even if what got on it from the semen has not been washed off.