What is the ruling on the wetness found in underwear; is it semen (mani) or prostatic fluid (madhi)? And can the wetness be considered either semen or prostatic fluid? What is the ruling on that according to more than one madhhab?

It is advisable to avoid masturbation due to its religious and physical harm.

If a sleeping person wakes up and finds wetness, and does not know whether it is maniy (seminal fluid) or madhiy (pre-seminal fluid):

- If there is an indication that it is madhiy (such as thinking about it before sleep or its widespread presence), then one should act accordingly. Otherwise, according to the Hanbalis, ghusl (ritual bath) is obligatory, as the default for discharge during sleep is that it is maniy.

- According to the Shafi'is, if one is certain it is maniy, then ghusl is performed. If one is certain it is madhiy, then wudu (ablution) is performed, and the clothes and body are purified. If there is doubt between the two, the relied-upon view is to choose between them.

- Some scholars (such as Qatadah, Mujahid, and Ibn Qudamah) held the view that ghusl is not obligatory in cases of doubt until one is certain that it is maniy.

- The Malikis held the view that ghusl is obligatory in cases of doubt, just as if it were certainly maniy.

In summary: If you are certain it is maniy, ghusl is obligatory. If you are certain it is madhiy, wudu is obligatory. If you are in doubt, it is more prudent to perform ghusl to resolve the difference of opinion.