Is ghusl obligatory for someone who finds wetness in their clothes but does not recall a wet dream, and does not know whether that wetness is semen or not?

What is found on clothes has several scenarios:

1. If it is most likely semen (with evidence such as color and smell), then ritual bathing (ghusl) is obligatory, and the prayers performed after finding the spot and before performing ghusl must be repeated. This is the preponderant opinion of the majority of scholars.

2. If it is most likely prostatic fluid (madhy), then the prayer is valid if the areas of the penis, clothes, and body affected by the madhy were washed, and one performed ablution (wudu) and prayed in clean clothes.

3. If the nature of the spot is unknown and there is doubt whether it is semen or madhy, the Muslim has a choice:

If he wishes, he can consider it semen, perform ghusl, and repeat the prayers.

And if he wishes, he can consider it madhy, in which case his prayer is valid if he washes the impurity of the madhy from his body and clothes, performs ablution, and prays in clean clothes. This choice is the view of the Shafi'i school.