What is the required waiting period before a husband resumes sexual relations with his adulterous wife?
Chapter on What is Prohibited to Marry and Combining Between Them and Other Matters
Al-Mughni
Book of Marriage
Primary text
It is required that the husband refrains from sexual intercourse with his wife until she has completed three menstrual cycles (Hayd) for purification (Istibra'). This is based on the narration of Rufay' ibn Thabit, who heard the Messenger of Allah, peace be upon him, say on the Day of Hunayn: 'It is not lawful for a man who believes in Allah and the Last Day to water the field of another,' meaning engaging in sexual relations with a pregnant woman. This prohibition also ensures that she does not bear a child resulting from adultery and ascribe it to him.
Supporting text
The opinion favoring one menstrual cycle for purification (Istibra') is sufficient, as one cycle suffices for female slaves and the Ummu Walad upon manumission. Since the text only mandates purification (Istibra'), and one cycle achieves this, it should be sufficient in this case.