What is the ruling on purity and clothing when one feels a drop descend during the ritual bath (ghusl) after masturbation? And do the dry bed and clothes that have been touched by semen or prostatic fluid become impure? And is it permissible to perform the Fajr prayer after the Friday prayer on Friday?

Masturbation is forbidden, and one must repent from it immediately. If you are unsure whether anything came out after masturbation, the default assumption is that nothing did. If you are certain that something did come out: if it was mani (seminal fluid), ghusl (ritual bath) is obligatory. If it was madhy (pre-seminal fluid), purification of it and wudu' (ablution) are obligatory. If you are in doubt about what came out, you may choose and assign it the ruling of whatever you wish. It is not obligatory to purify clothes except for prayer. As for the body, it must be purified immediately. Sleeping on an impure bed is permissible, though purifying it is recommended. Mani (seminal fluid) is pure; it is not obligatory to wash it. Delaying prayer and not performing ghusl until the time for prayer expires is a grave sin. Performing a missed prayer during the Friday sermon is permissible.