Should I Repeat Prayer If I Forgot Ghusl?
When performing ghusl becomes due, because of a janabah (i.e., ritual impurity due to sexual defilement), menses, etc., a Muslim should hasten to do it, since being ritually impure keeps the Muslim unable to perform various acts of worship that require ritual purity. If a person wants to delay it for some unavoidable reason, he or she may do wudu’ in order to lessen the impurity. It is reported on the authority of `Ammar ibn Yasser (may Allah be pleased with him) that Prophet Muhammad (peace and blessings be upon him) permitted a person in a state of janabah, if he or she wants to eat, drink, or sleep, to perform the wudu’ of Prayer (At-Tirmidhi).
The late sheikh `Abdul-`Aziz Ibn Baz, a renowned Muslim scholar, stated,
If a Muslim remembers that he or she had a wet dream and ejaculated semen, then he or she must offer ghusl for janabah and repeat the Prayers that he or she has offered during the time between the wet dream and doing ghusl.