Musannaf Ibn Abi Shayba 9:770

Ibn Fudayl narrated to us, from Isa ibn Yasar, from Sa’id ibn al-Musayyib, regarding His saying: "Your wives are a tilth for you, so come to your tilth when or how you will." He said: "If you wish, practice withdrawal (al-azl), and if you wish, do not practice withdrawal."