"When the Messenger of Allah (ﷺ) got up at night, he would brush his mouth with the Siwak."
Sunan an-Nasa'i Book 1, Hadith 2
← Previous Hadith "When any one of you wakes from sleep, let him not dip his hand in (the water he uses for) his Wudu' until he has washed it three times, for none of you knows where his hand spent the night."

Sunan an-Nasa'i Book 1, Hadith 1 Next Hadith → "I came to the Messenger of Allah (ﷺ) when he was using the Siwak, and the end of the Siwak was on his toungue, and he was saying, "'A','a'."

Sunan an-Nasa'i Book 1, Hadith 3