Allah's Messenger said: "If it were not that it would be difficult on my nation, then I would have ordered them to use the Siwak for each prayer."
Jami` at-Tirmidhi Book 1, Hadith 22
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Jami` at-Tirmidhi Book 1, Hadith 21 Next Hadith → 'I heard Allah's Messenger saying: 'If it were not that it would be difficult on my nation then, I would have ordered them to use the Siwak for each prayer and to delay the Isha prayer until the third of the night.'"He said: Zaid bin Khalid wouId attend the prayer in the Masjid and his Siwak would be on his ear in the location of the pen on the ear of a writer. He would not get up to pray without cleaning his teeth, then returning it to its location."

Jami` at-Tirmidhi Book 1, Hadith 23