It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever performs ablution should clean his nose by blowing it out, and whoever uses stones (to clean himself) should use an odd number."
(b) Another narration from Sayyiduna Abu Hurayrah (may Allah be pleased with him) is reported likewise.
(c) From Sayyiduna Jabir (may Allah be pleased with him) the same is reported concerning the use of stones.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 504