Musnad Abu Ya'la al-Mawsili 110:227

Zuhayr narrated to us, Hashim ibn al-Qasim narrated to us, Warqa’ ibn ‘Umar al-Yashkuri narrated to us, he said: I heard ‘Ubayd Allah ibn Abi Yazid narrating from Ibn ‘Abbas, he said: The Messenger of Allah (may Allah bless him and grant him peace) came to the privy, so I placed water for his ablution for him. When he came out, he said: "Who placed this?" They said: "Ibn ‘Abbas." He said: "O Allah, grant him understanding [in religion]."