Musannaf Ibn Abi Shayba 1:274

Yahya ibn Salim al-Ta'ifi narrated to us, from Isma'il ibn Kathir, from 'Asim ibn Laqit ibn Sabira, from his father, who said: I said, "O Messenger of Allah, inform me about ablution (wudu)." He said, "Perform the ablution thoroughly, and be thorough in sniffing water into the nose (istinshaq), unless you are fasting."