The Messenger of Allah ﷺ said, "Whoever does not trim his moustache is not one of us."
أخبرنا علي بن حجر قال أنبأنا عبيدة بن حميد عن يوسف بن صهيب عن حبيب بن يسار
قال رسول الله ﷺ من لم يأخذ شاربه فليس منا
Sahih. Tirmidhi narrated it in the Book of Manners, the chapter on trimming the mustache, hadith (2761), from the report of Ubayda, and he was followed by Yahya bin Saeed Qattan as recorded by Tirmidhi, hadith (2761), and by Mutamir bin Sulayman as recorded by Nasai (Sughra, 5050). Tirmidhi said it is hasan sahih, and Ibn Hibban graded it sahih (Mawarid, 1481).