Abu Huraira (may Allah be pleased with him) reports that the Messenger of Allah (peace and blessings be upon him) said: When anyone performs ablution, he should rinse his nose with water and expel it, and the one performing istinja should use an odd number of clods.
Hadith Referenceالمنتقى ابن الجارود / كتاب الطهارة / 39