What is the ruling on the prayer of a disbeliever who embraced Islam and prayed before performing ghusl, knowing the obligation of ghusl but unaware of its obligation before prayer, then doubted it but paid no attention, then became certain, performed ghusl, and completed his prayer?

The gist of the fatwa is: The preponderant opinion according to us is that a disbeliever must perform ghusl (ritual bath) if, while in a state of disbelief, they committed an act necessitating ghusl; otherwise, it is not obligatory. If they performed ghusl upon embracing Islam, then what is prohibited for a person in a state of major ritual impurity (junub) is prohibited for them until they perform ghusl. Therefore, if they committed an act while in a state of disbelief that necessitated ghusl, their prayer is not valid until they perform ghusl; otherwise, their prayer is valid.