"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.
Sunan an-Nasa'i Book 27, Hadith 109
← Previous Hadith "While I was with Abu Hurairah he said: 'A woman came to the Messenger of Allah and said: May my father and mother be ransomed for you! My husband wants to take my son away, but he helps me, and brings me water from the well of Abu 'Inabah. Her husband came and said: Who is going to take my son from me? The Messenger of Allah said: "O boy, this is your father and this is your mother; take the hand of whichever of them you want." He took his mother's hand and she left with him.'"

Sunan an-Nasa'i Book 27, Hadith 108 Next Hadith → "I said to her: 'Tell me your Hadith.' She said: 'I was separated from husband by Khul', then I came to 'Uthman and asked him: What 'Iddah do I have to observe? He said: You do not have to observe any 'Iddah, unless you had intercourse with him recently, in which case you should stay with him until you have menstruated. He said: In that I am following the ruling of the Messenger of Allah concerning Mariam Al-Maghaliyyah, who was married to Thabit bin Qais and was separated by Khul' from him.'"

Sunan an-Nasa'i Book 27, Hadith 110