Musannaf Ibn Abi Shayba 3:1728

Waki’ narrated to us, from Isra’il, from Dirar ibn Murrah, from ‘Abdullah ibn Abi al-Hudhayl al-‘Anazi, he said: ‘Umar said: "Were it not that it would become a Sunnah (a precedent), I would have given permission (for it)."