1t was narrated that Abuz-Zarrad said: Ja"far bin Tammam bin "Abbas narrated to me that his father said:

They came to the Prophet (ﷺ) , or someone came to him, and he said: “Why do I see you coming to me with yellow and dirty teeth? Use the siwak. Were it not that it would be too difficult for my ummah, I would have obliged them to use the siwak as I have obliged them to do wudoo’."