Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa. – Question No.8 of Fatwa No.7293
Question: If a man shaves his moustache and leaves his beard (to grow), is there any sin in this? And what did the Messenger (sal-Allaahu ‘alayhi wa sallam) used to do?
Response: All Praise is for Allaah the One, and prayers and salutations upon His Messenger, upon his family and his companions. To proceed…
The Sunnah is to trim the moustache and not to remove it as the Prophet (sal-Allaahu ‘alayhi wa sallam) said:
«Trim the moustaches and leave the beards [to grow] and oppose (differ) from the mushrikoon». The authenticity of this hadeeth is agreed upon by al-Bukhaaree and Muslim.
If he shaved it [off] then there is nothing (no sin) upon him. As for the beard, then it is obligatory to leave it (to grow) as the Prophet (sal-Allaahu ‘alayhi wa sallam) said:
«Trim the moustaches and leave the beards [to grow], [in doing so] oppose (differ from) the mushrikoon».
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet (sal-Allaahu ‘alayhi wa sallam) and his family and his companions.