Sayyiduna Abu Huraira (may Allah be pleased with him) narrated from the Messenger of Allah (peace and blessings be upon him), he (peace be upon him) said: "Whoever performs ablution should clean his nose, and whoever uses stones for istinja should use an odd number of stones."
Hadith Referenceمسند اسحاق بن راهويه / كتاب الطهارة / 100
Hadith Takhrij«مسلم ، باب الايتار اسنتشار والستجمار ، رقم : 298»