سنن النسائي

It was narrated from 'Abdullah that he said: "The Sunnah divorce is a divorce issued when she is pure (not menstruating) without having had intercourse with her. If she menstruates and becomes pure again, give her another divorce, and if she menstruates and becomes pure again, give her another divorce, then after that, she should wait for another menstrual cycle." (One of the narrators) Al-A'mash said: "I asked Ibrahim, and he said something similar."