Musannaf Ibn Abi Shayba 9:773

Waki’ narrated to us, from Abu Hanifa, from Kathir al-Rammah, from Abu Dhira’, who said: I asked Ibn Umar about the saying of Allah, the Exalted: "So come to your tilth when or how you will," and he said: "If you wish, practice withdrawal (al-azl), and if you wish, do not practice withdrawal."