Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 49
Narated By Abu Burdah on the authority of his father Abu Musa al-Ashari according to the version of Musaddad : We came to the Apostle of Allah (pbuh) to provide us with a mount, and found him using the tooth-stick, its one end being at his tongue (i.e. he was rinsing his mouth).
According to the version of Sulaiman it goes: I entered upon the Prophet (pbuh) who was using the tooth-stick and had placed it at one side of his tongue, producing a gurgling sound.
Abu Dawud said: Musaddad said that the tradition was lengthy but he shortened it.