Consultation:
A fasting person is unaware that he is junub. In the afternoon, he notice and performs ghusl by immersion. Does this invalidate his fast? And if he realizes what he has done only after performing the ghusl, does he have to perform the qada of the fast?

Answer:
if one performs ghusl by immersion out of forgetfulness (of the fact that he is fasting) or unintentionally, then both his fast and ghusl are valid; thus, he does not have to perform the qada of the fast.