´AR-Rubayyi bint Mu'awwidh bin Al-Afra narrated:` that she got a Khul during the time of the Prophet. So the Prophet ordered her - or: she was ordered - that she observe an Iddah of a menstruation."
1؎: «خلع» is derived from «خلع الثوب», which means "to remove clothing." In the terminology of Islamic law (shar‘i istilah), «خلع» refers to a woman separating from her husband by returning the property (mahr) given to her as dower.
2؎: The hadith of the chapter supports the view that «خلع» is not a divorce (talaq) but an annulment (fasakh), and the waiting period (‘iddah) for «مختلعہ» is one menstrual cycle. Those who say that «خلع» is not an annulment but a divorce maintain that the waiting period for «مختلعہ» is the same as that of a divorced woman. The preferred (rajih) opinion is the first one, which is in accordance with both these hadiths.
´Ar-Rubayy' bint Mu'awwidh bin 'Afra' narrated that Thabit bin Qais bin Shammas hit his wife and broke her arm --her name was Jamilah bint 'Abdullah bin Ubayy. Her brother came to the Messenger of Allah to complain about him, and the Messenger of Allah sent for Thabit and said:` "Take what she owes you and let her go." He said: "Yes." And the Messenger of Allah ordered her to wait for one menstrual cycle and then go to her family.
Hafiz Muhammad Ameen
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.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 3527