Shaving the beard is haraam because of the saheeh ahaadeeth that clearly state this, and because of the general application of texts that forbid resembling the kuffaar. One of these reports is the hadeeth of Ibn ‘Umar who said that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Be different from the mushrikeen: let your beards grow and trim your moustaches.” According to another report: “Trim your moustaches and let your beards grow.”
There are other hadeeth which convey the same meaning, which is to leave the beard as it is and let it grow long, without shaving, plucking or cutting any part of it. Ibn Hazm reported that there was scholarly consensus that it is an obligation (fard) to trim the moustache and let the beard grow. He quoted a number of ahaadeeth as evidence, including the hadeeth of Ibn ‘Umar (may Allaah be pleased with him) quoted above, and the hadeeth of Zayd ibn Arqam in which the Prophet (peace and blessings of Allaah be upon him) said: “Whoever does not remove any of his moustache is not one of us.” (Classed as saheeh by al-Tirmidhi). Ibn Hazm said in al-Furoo’: “This is the way of our colleagues [i.e., the Hanbalis].”
Is it haraam (to shave it)? Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him) said: “The Qur’aan, Sunnah and ijmaa’ (scholarly consensus) all indicate that we must differ from the kuffaar in all aspects and not imitate them, because imitating them on the outside will make us imitate them in their bad deeds and habits, and even in beliefs, which will result in befriending them in our hearts, just as loving them in our hearts will lead to imitating them on the outside. Al-Tirmidhi reported that the Messenger of Allaah (peace and blessings of Allaah be upon him) said, “He is not one of us who imitates people other than us. Do not imitate the Jews and Christians.” According to another version: “Whoever imitates a people is one of them.” (Reported by Imaam Ahmad) ‘Umar ibn al-Khattaab rejected the testimony of the person who plucked his beard. Imaam Ibn ‘Abd al-Barr said in al-Tamheed: “It is forbidden to shave the beard, and no one does this except men who are effeminate” i.e., those who imitate women. The Prophet (peace and blessings of Allaah be upon him) had a thick beard (reported by Muslim from Jaabir). It is not permitted to remove any part of the beard because of the general meaning of the texts which forbid doing so.
Fataawa al-Lajnah al-Daa’imah, 5/133