Musannaf Ibn Abi Shayba 27:471

'Abdah ibn Sulayman narrated to us, from 'Abd al-Malik ibn Abi Sulayman, who said: I said to 'Ata': "Was there anyone among the companions of the Messenger of Allah, may Allah bless him and grant him peace, more knowledgeable than 'Ali?" He said: "No, by Allah, I do not know of any."