Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 50
Narated By 'Aisha, Ummul Mu'minin : The Apostle of Allah (pbuh) was using the tooth-stick, when two men, one older than the other, were with him. A revelation came to him about the merit of using the tooth-stick. He was asked to show proper respect and give it to the elder of the two.