Musannaf Ibn Abi Shayba 1:576

576. Isa ibn Yunus narrated to us, from al-Taymi, from Abu Mijlaz, who said: I saw Ibn Umar clipping his nails, so I said to him, "You are clipping your nails and you do not perform wudu?" He said, "How clever you are! You are cleverer than the one whom his family named 'Kays' (clever)."