Narrated Abu Burdah (radiyallaahu-anhu): “I came to the Prophet (sallal-laahu-alayhi-wasallam) and saw him carrying a Siwaak in his hand and cleaning his teeth, saying, ‘’U’’ ‘’U‟, as if he was retching while the Siwaak was in his mouth”. [Bukhaari Vol 1. Hadeeth Number 244]

In the narration of Abu Moosaa (radiyallaahu-anhu): ‘’I entered upon the Prophet (sallal-laahu-alayhi-wasallam) and the edge of the Siwaak was on his tongue’’. [Saheeh Muslim Number: 592]

Imaam Sadi (rahimahullaah) said: In this (hadeeth) is (proof) that the siwaak can be (used) on the tongue, just as it can be (used) on the gums and the teeth. [Sharh Umdatul Ahkaam’ page 69. 1st edition Dar At-Tawheed 2010/ 1431]