Musnad Ahmad 30:628

'Abd al-Razzaq narrated to us, Malik narrated to us, from Abu al-Zinad, from al-A'raj, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), who said: "When one of you performs ablution, let him put water in his nose, then let him blow it out. And whoever cleans himself with stones (istijmar), let him use an odd number."