Sunan Abi dawud:49 Chapter: Seclusion While Relieving Oneself Book 1, Hadith 49

Narrated Abu Burdah: On the authority of his father ( Abu Musa al-Ash’ari), reported (according to the version of Musaddad) : We came to the Apostle of Allaah (sal Allaahu alayhi wa sallam) to provide us with a mount, and found him using the tooth-stick, its one end being at his tongue (i.e. he wsa rinsing his mouth). According to the version of Sulaiman it goes : I entered upon the Prophet (sal Allaahu alayhi wa sallam ) who was using the tooth-stick, and had it placed at one side of his tongue, producing a gurgling sound. Abu Dawud said : Musaddad said that the tradition was a lengthy but he shortened it.