"The Messenger of Allah (ﷺ) said: 'Whoever does not trim his mustache, he is not from one of us.'"
Sunan an-Nasa'i Book 1, Hadith 13
← Previous Hadith "The deeds connected to the Fitrah are: Clipping the nails, removing the mustache and shaving the pubes."

Sunan an-Nasa'i Book 1, Hadith 12 Next Hadith → "A time limit was set for us, by the Messenger of Allah (ﷺ), regarding trimming the mustache, clipping the nails and plucking the pubes; we were not to leave that for more than forty days," on one occasion he said: "Forty nights."

Sunan an-Nasa'i Book 1, Hadith 14