It is narrated from Sayyiduna Uqbah bin Amir (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you applies kohl, let him apply it an odd number of times; and when he cleans himself after relieving himself, let him use an odd number of stones."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15004