Hadith 682:2
Jarir ibn Abd al-Hamid narrated to us, from Mansur, from Hilal, from Salamah ibn Qays, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When you perform ablution (wudu), then perform istinthar (expelling water from the nose). And when you perform istijmar (cleaning oneself with stones), then do it an odd number of times."
حدثنا جرير بن عبد الحميد، عن منصور، عن هلال، عن سلمة بن قيس قال: قال رسول الله صلى الله عليه وسلم: " إذا توضأت فانتثر ، وإذا استجمرت فأوتر "