Al-Mughnī (3/293–294) states: In summary, performing ghusl (ritual bathing) when entering ihrām is legislated for women just as it is for men, for it is a devotional rite. It is even more emphatically required of a menstruating woman or one undergoing post-natal bleeding, because explicit reports address their case. Jābir said: “When we reached Dhul-Ḥulayfah, Asmāʾ bint ʿUmays gave birth to Muḥammad ibn Abī Bakr. She sent word to the Messenger of Allah ﷺ asking, ‘What should I do?’ He replied, ‘Perform ghusl, bind yourself with a cloth, and enter ihrām.’” (1) Ibn ʿAbbās relates that the Prophet ﷺ said: “When a woman in post-natal bleeding or menstruation reaches the appointed miqāt, she must enter ihrām and carry out all the rites except the circumambulation of the House.” (2) The Prophet ﷺ likewise instructed ʿĀʾishah to bathe before raising her voice with the talbiyah of Hajj while she was menstruating. End quote.

The wisdom behind the ghusl of a menstruating or post-natal woman at the start of ihrām is cleanliness, eliminating offensive odors so as not to trouble people when they gather, and reducing impurity. Should menstruation or post-natal bleeding begin after they have already entered ihrām, that has no effect on their consecration: they remain in ihrām, avoid its prohibitions, and do not perform tawāf until they have become pure and bathed. If the Day of ʿArafah arrives before they have purified themselves, and they had first assumed ihrām for ʿUmrah with the intention of tamattuʿ (ʿUmrah followed by Hajj), then they must assume ihrām for Hajj at that point.