Must a woman who did not observe the waiting period (iddah) after a death or divorce make it up later, and what is the expiation for one who abandoned it due to ignorance, or negligence, or lack of faith in it?

The waiting period ('iddah (definition)) is a duration prescribed by Islamic law for a woman after separation from her husband. The 'iddah begins from the moment its cause occurs (divorce or death), even if the woman does not learn of the cause until later. When the days of the 'iddah expire, it is not to be made up if the woman did not observe it. A woman is considered sinful if she neglects the rulings of the 'iddah while knowing them. As for one who does not believe in the 'iddah at all, she is a disbeliever, because she denies the Qur'an, the Sunnah (definition), and the consensus of the Muslims.