It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that five things are from the natural Sunnah: cutting the nails, trimming the moustache, plucking the hair of the armpits, shaving the hair below the navel, and circumcision.

Said al-Musayyib that it was Ibrahim (peace be upon him) who first hosted a guest, and he was the first to perform circumcision, and the first to trim the mustache, and the first to see a white hair and say: "O Lord! What is this?" Allah, Glorious and Exalted, said: "This is dignity and respect." Ibrahim (peace be upon him) said: "So O Lord! Increase me in dignity."

Imam Malik, may Allah have mercy on him, said that the moustache should be trimmed so much that the edges of the lips become visible, but it should not be trimmed off completely.