It is narrated from Sayyiduna Qutham or Tamam that once we were present in the service of the Prophet (peace be upon him), and the Prophet (peace be upon him) said: What is the matter, why do I see your teeth yellow and discolored? Do you not use the miswak? If it were not difficult for my ummah, I would have made the use of miswak obligatory for them just as wudu is obligatory.