Yahya related to me from Malik from Abu'zZinad from al-Araj fromAbu Hurayra that the Messenger of Allah, may Allah bless him and granthim peace, said, "When you do wudu, snuff water into your nose andblow it out, and if you use stones to clean your private parts use anodd number."
USC-MSA web (English) reference: Book 2, Hadith 2
Arabic reference: Book 2, Hadith 34