Is it permissible for a fasting person to sleep in a state of major ritual impurity (janābah) until after the dawn (Fajr) call to prayer, and is he required to hasten his ritual bath (ghusl), and what are the implications of that?

It is recommended for a person in a state of ritual impurity (junub) during the nights of Ramadan to perform ghusl before Fajr. However, if Fajr overtakes him while he is still in a state of ritual impurity, his fasting is valid, and he only needs to perform ghusl. The proof for this is that the Prophet, peace and blessings be upon him, used to wake up in a state of ritual impurity due to sexual intercourse, then perform ghusl and fast.