"Whenever the Messenger of Allah got up for prayer at night to pray Tahajjud (night optional prayer), he would clean his mouth with the tooth stick."
Sunan Ibn Majah Book 1, Hadith 20
← Previous Hadith "I saw 'Uthman bin 'Affan sitting in Maqa'id. He called for water and he performed ablution, the he said: 'I saw the Messenger of Allah sitting in this place where I am sitting, performing ablution as I have done. Then he said: "Whoever performs ablution as I have done, his previous sins will be forgiven." And the Messenger of Allah said: "And do not be conceited (due to this great virtue)." (Sahih)

Another chain with similar wording.

Sunan Ibn Majah Book 1, Hadith 19 Next Hadith → "The Messenger of Allah said: 'Were it not that it would be too difficult for my Ummah (nation), I would have commanded them to use the tooth stick at every time of prayer.'"

Sunan Ibn Majah Book 1, Hadith 21