Growing the beard is an act of obedience.
Allah, the Exalted, says: “It is not for a believing man or a believing woman—once Allah and His Messenger have decided a matter—to claim any choice concerning it.” ⦗Al-Ahzab 33:36⦘
He also says: “Let those who oppose his command beware, lest a trial befall them or a painful punishment strike them.” ⦗An-Nur 24:63⦘
One of the matters that the Messenger of Allah ﷺ expressly commanded is the growing of the beard (1). Ibn ʿUmar narrated that the Prophet ﷺ “ordered the trimming of the moustaches and the growing of the beard.” ⦗Muslim⦘
Abu Hurayrah reported that the Messenger of Allah ﷺ said: “Cut back the moustaches and leave the beards; differ from the Magians.” ⦗Muslim⦘
When the Prophet ﷺ saw the two envoys of Chosroes who had shaved their beards and allowed their moustaches to grow long, he was repelled from even looking at them and said: