Yahya related to me from Malik from Abu Bakr ibn Nafi from his father Nafi from Abdullah ibn Umar that the Messenger of Allah, may Allah bless him and grant him peace, ordered the moustache to be trimmed and the beard to be left.
Muwatta Malik Book 51, Hadith 1
← Previous Hadith "There is no contagion, no hama and no serpent in a hungry belly. However, the possessor of sick livestock must not stop at the same place as the possessor of healthy livestock, but the possessor of healthy livestock may stop wherever he wishes."

They said, "Messenger of Allah, Why is that?" The Messenger of Allah, may Allah bless him and grant him peace, said, "It is harmful."

Note: The majority of scholars interpret this to mean that these things in and of themselves do not transmit or cause harm through supernatural or hidden means but that Allah is ultimately in control and any fearful superstition around these is false.

Muwatta Malik Book 50, Hadith 19 Next Hadith → Yahya related to me from Malik from Ibn Shihab that Humay ibn Abd ar-Rahman ibn Awf heard Muawiya ibn Abi Sufyan say from the mimbar in the year that he performed the hajj, holding a lock of hair (i.e. a hairpiece) which he took from one of his guards, "People of Madina! Where are your learned men? I heard the Messenger of Allah, may Allah bless him and grant him peace, forbid the like of this, saying, 'The Banu Israil were destroyed when their women started to use this.' "

Muwatta Malik Book 51, Hadith 2