Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 51
Narated By 'Aisha, Ummul Mu'minin : The Apostle of Allah (pbuh) was accustomed to use the tooth-stick and then give it to me to wash it. I would first use it myself, then wash it and hand it over to him.