What is the viscous fluid that is discharged during sleep?

The viscous fluid seen by a sleeper has three states: 1- It could be semen (maniy), in which case ghusl (ritual bath) is obligatory, and all prayers performed before ghusl must be repeated. 2- It could be prostatic fluid (madhiy), in which case the prayer is valid if the madhiy is washed from the male organ and clothes, and one performs wudu (ablution) and prays in clean clothes. 3- Its true nature could be unknown, in which case one has the choice: either consider it semen, perform ghusl, and repeat the prayers, or consider it prostatic fluid, in which case the prayer is valid if the madhiy is washed, one performs wudu, and prays in clean clothes. This detailed explanation is the fatwa adopted by the Shafi'i school.