What is the ruling on one who leaves the prayer out of forgetfulness?

Question:
And if one did not pray Maghrib, when does he make it up?

Answer:
He makes it up whenever he remembers it. If a person misses an obligatory prayer because he forgot it or fell asleep, he prays it as soon as he remembers it, at whatever time he remembers it. The Prophet (peace and blessings be upon him) said: There is no expiation for it except that. The sleep referred to here is incidental sleep, the kind that happens to a person without his intention. As for the one who deliberately sleeps in order to miss the prayer, his prayer does not suffice for him, even if he prays it after the time has passed, because he intentionally caused it to be missed outside its time. He must repent to Allah and strive to maintain the prayers within their times.