Is masturbation permissible, and is prayer after it with ablution permissible, and what is the required word for repentance?

Masturbation is religiously forbidden (haram), for Allah has permitted sexual enjoyment only through one's wife or female slave (malak al-yamin). Whoever seeks beyond that is an transgressor.

Regarding the ruling on the prayer of one who practices it: if semen is ejaculated, ghusl (ritual bath) is obligatory. If madhy (pre-seminal fluid) is discharged, washing the penis and performing wudu (ablution) are obligatory. If nothing is discharged, wudu suffices. Any prayers performed without purification must be repeated.

As for repentance, its essence is seeking forgiveness (istighfar), and its conditions are: immediate cessation of the sin, remorse for it, and a firm resolve not to return to it.