Each and every believer is commanded to follow the commandments of Allah [Subhanahu Wataa’la(SW)] and His messenger[Sallah llahu A’layh Wasallam(SAW)]. Allah says “…Obey Allah and the messenger…”3:32, 5: 92, 8: 1 etc.
Moreover without the prophet’s sayings the Qur’an could have been almost impossible to comprehend. Hence following the tradition /way (Sunnah) of the prophet is one of the obligations of each and every Muslim that they may fully understand Islam. Some of these traditions of the prophet are obligatory to follow hence they carry the weight equal to the commandments of Allah because Allah says “…And whatsoever the Messenger gives you, take it; and
Whatsoever he forbids you, abstain (from it). Have Taqwa of Allah; verily, Allah is Severe in punishment.” 59:7.
It was proven that the Messenger of Allah (SAW) commanded men to leave the beard alone and let it grow naturally. There are narrations that ‘Abd-Allaah ibn ‘Umar (may Allah be pleased with him) said: the Messenger of Allah (SAW) said: “Trim the moustache and leave the beard.” Narrated by al-Bukhaari, 5443; Muslim, 600. Yet in another hadeeth the prophet said “Be different from the mushrikeen: cut the moustache and let the beard grow.” Narrated by Muslim, 602.
The evidence of leaving the beard is so overwhelming that Abu Hurayrah (may Allaah be pleased with him) said: The Messenger of Allaah (SAW) said: “Trim the moustache and let the beard grow; be different from the Magians (Zoroastrians).” Muslim (383)
Therefore based on the information above it is (according to many renown scholars) haraam to shave the beard and keep the moustache. By stating that it is haraam, it means if you do it then you are sinning.
Many men or boys do double standards by talking about the mischievous act of women or girls of not wearing hijab, but they turn the blind eye on the obligation of keeping beard and trimming the moustache that has been prescribed to them. Am not condoning the bad act of not putting on hijaab by sisters but my question to males is ‘how do you feel to always pinpoint the sins of others while you yourselves fall in the same category?
A lot of people don’t keep beard just because, according to them, they want to look good in front of other people. It should be noted here that good looks in Islam is not based on the so-called beauty which appeals to sick minds which are enamoured of kaafir fashions and the appearance of corrupt people such as male and female actors and singers, or fashion models, rather it is based on Islamic beautification for example keeping clean, wearing perfume (for men), combing and other beautifications allowed in Islam.
Allah knows best