Musnad Ahmad 30:2087

Ali ibn Ishaq narrated to us, Abdullah informed us, Yunus informed us, from al-Zuhri, Abu Idris al-Khawlani informed me that he heard Abu Hurairah saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever performs ablution, let him rinse his nose (with water and expel it). And whoever cleans himself with stones (after defecation), let him use an odd number."