Sunan Abi Dawud, Book 1, Hadith 49 (USC-MSA)

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.

حَدَّثَنَا مُسَدَّدٌ، وَسُلَيْمَانُ بْنُ دَاوُدَ الْعَتَكِيُّ، قَالاَ حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ غَيْلاَنَ بْنِ جَرِيرٍ، عَنْ أَبِي بُرْدَةَ، عَنْ أَبِيهِ، قَالَ مُسَدَّدٌ قَالَ أَتَيْنَا رَسُولَ اللَّهِ صلى الله عليه وسلم نَسْتَحْمِلُهُ فَرَأَيْتُهُ يَسْتَاكُ عَلَى لِسَانِهِ - قَالَ أَبُو دَاوُدَ وَقَالَ سُلَيْمَانُ قَالَ دَخَلْتُ عَلَى النَّبِيِّ صلى الله عليه وسلم وَهُوَ يَسْتَاكُ وَقَدْ وَضَعَ السِّوَاكَ عَلَى طَرَفِ لِسَانِهِ - وَهُوَ يَقُولُ ‏ "‏ إِهْ إِهْ ‏" ‏ ‏.‏ يَعْنِي يَتَهَوَّعُ ‏.‏ قَالَ أَبُو دَاوُدَ قَالَ مُسَدَّدٌ فَكَانَ حَدِيثًا طَوِيلاً اخْتَصَرْتُهُ ‏.‏

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also referenced under: Hadith 49 (DarusSalam) & Hadith 49 (Hasan)