Musannaf Ibn Abi Shaybah

Hazrat Amir (may Allah have mercy on him) and Hazrat Hakam (may Allah have mercy on him) say that if a man says to his wife, "When you menstruate, you are divorced," then her menstruation stops and she becomes pregnant, the man can have intercourse with her until she menstruates. Hazrat Amir (may Allah have mercy on him) says that if this is valid in the near term, it is also valid in the distant term.