Does the divorce issued by the husband take effect if it occurred three weeks after childbirth, when the post-natal bleeding (nifas) had stopped but the wife had not yet performed ghusl (ritual purification)? And how should her 'iddah (waiting period) be calculated if the divorce takes effect?

Divorce during postpartum bleeding (nifas) is impermissible and, according to the soundest opinion, does not take effect. However, if the postpartum bleeding stops and the woman is deemed pure, then the divorce takes effect, even if she has not yet performed ghusl (ritual bath), because purity is attained by the cessation of blood and complete dryness, or by seeing the white discharge (al-qassah al-bayda'). This is supported by the hadith of Ibn Umar, who divorced his wife while she was menstruating. The Prophet, peace and blessings be upon him, commanded him to take her back and then divorce her when she was pure or pregnant. If the divorce takes effect, the waiting period (iddah) begins with the first menstruation after purity and ends with purity from the third menstruation and performing ghusl thereafter.