Silsilat al-Ahadith al-Sahihah

Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates that the Messenger of Allah (peace and blessings be upon him) was mentioned in the presence of the Magians. The Prophet (peace and blessings be upon him) said: "These (Magians) let their mustaches grow and shave their beards, so you should oppose them." Thus, Sayyiduna Ibn Umar (may Allah be pleased with them both) used to trim his mustache in such a way as the hair of a goat or camel is trimmed.

Sayyiduna Abu Umamah (may Allah be pleased with him) says: The Messenger of Allah (peace and blessings be upon him) came to some Ansaris with white beards and said: "O group of Ansaris! (Color your white hair) red or yellow and oppose the People of the Book." They said: O Messenger of Allah! Indeed, the People of the Book trim their beards and grow their mustaches. The Messenger of Allah (peace and blessings be upon him) said: "You grow your beards and trim your mustaches and oppose the People of the Book." They said: O Messenger of Allah! Indeed, the People of the Book used to wear leather socks and not wear shoes. He (peace and blessings be upon him) said: "You wear shoes as well as socks and oppose the People of the Book."