Musnad Ahmad 723:5

'Abd al-Razzaq narrated to us, Ma'mar and al-Thawri narrated to us, from Mansur, from Hilal ibn Yasaf, from Salamah ibn Qays, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said to me: "When you perform ablution (wudu), then rinse your nose (istinthar). And when you clean yourself with stones (istijmar), then use an odd number."