It was narrated from 'Asim bin Laqit bin Sabrah that his father said:
"I said: 'O Messenger of Allah! Tell me about ablution.' He said: 'Perform ablution properly and sniff water up into your nostrils, thoroughly, unless you are fasting.'"
English reference: Vol. 1, Book 1, Hadith 407
Arabic reference: Book 1, Hadith 441