If the Messenger (peace be upon him) commanded us to grow our beards out to differentiate ourselves from the Majus and the disbelievers, is it then obligatory to trim it to further differentiate ourselves from them?

The Prophet, peace and blessings be upon him, commanded the letting of the beard grow and its full growth in order to differ from the disbelievers. Authentic hadiths have been narrated to this effect. In Sahih al-Bukhari, on the authority of Ibn Umar: "Differ from the polytheists, let your beards grow full, and trim your mustaches." In Sahih Muslim, on the authority of Abu Hurairah: "Trim the mustaches, and let the beards hang down; differ from the Magians." In Musnad Ahmad, also on his authority: "Let your beards grow, trim your mustaches, change your grey hair, and do not resemble the Jews and Christians."

The purpose of this is twofold: First: To differ from the disbelievers who shave their beards. Second: To conform to the prophets and act in accordance with the natural disposition (fitra), for letting the beard grow is part of the guidance of the prophets and among the practices of the natural disposition. If the first purpose ceases to exist, the second purpose remains valid.