Zayd bin Arqam reported that the Prophet ﷺ said, "Whoever does not trim his moustache is not one of us."
عن النبي ﷺ قال: من لم يأخذ من شاربه فليس منا.
Tirmidhi (2761), Nasai (5047), and Ahmad (19263) all narrated it from the hadith of Yusuf bin Suhayb, from Habib bin Yasar, from Zayd bin Arqam, who related it. Its chain of transmission is sahih. Tirmidhi said, "This is a hasan sahih hadith." His saying, "he is not one of us," means he is not following our sunnah.