Musannaf Ibn Abi Shayba 1:84

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