Musannaf Ibn Abi Shayba 9:879

Waki’ narrated to us, from Sharik, from ‘Urwah, from ‘Abdullah ibn Bashir, from Abu al-Ash’ath, from Ibn ‘Umar, who said: Its beginning is *sifah* (fornication/illicit intercourse) and its end is *nikah* (marriage), and its beginning is *haram* (forbidden) and its end is *halal* (lawful).