Nasai

Since khul‘ (خلع) is a dissolution (faskh) of marriage, its waiting period (‘iddah) is one menstrual cycle (hayd), and that too only for the purpose of ascertaining the condition of the womb—that is, to determine whether the woman is pregnant or not. If she is pregnant, then she may remarry after childbirth (wada‘ al-haml). And if she is not pregnant, then after one menstrual cycle. This explicit ruling is also transmitted from Ibn ‘Abbas and ‘Uthman (radi Allahu anhuma). This is likewise the position of Imam al-Shafi‘i, Ahmad ibn Hanbal, and Ishaq ibn Rahwayh (rahimahumullah). According to the Hanafis, khul‘ is a divorce (talaq), so they say its waiting period is three menstrual cycles, but their position is rejected because it is contrary to authentic ahadith.