Musannaf Ibn Abi Shayba 9:760

Abu Bakr ibn Ayyash narrated to us, from Abu Ishaq, from Za'idah ibn Umayr, from Ibn Abbas, regarding the saying of Allah, "Your wives are a tilth for you": He said: "Whoever wishes to practice coitus interruptus (azl), let him practice it, and whoever wishes not to practice it, let him not practice it."