Musnad Ahmad 723:1

Sufyan ibn 'Uyaynah 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: "When you perform wudu, then rinse your nose (by inhaling water). And when you use stones for cleaning (istijmar), then use an odd number."