How can one respond to those who say that the beard was a social phenomenon during the time of the Messenger of Allah, peace and blessings be upon him, and that religion is in the heart, and that the beard is merely superficial and means nothing?

A distinction must be made between acts of worship (ibadat) and customs (adat). Acts of worship vary according to what they relate to (body, wealth, appearance, and clothing), and an act of worship is recognized by the legal commands and requirements associated with it. For example, the Prophet's (peace and blessings be upon him) prohibition of gold and silk for men transformed their avoidance into an act of worship. Similarly, growing a beard: if it were merely a custom, the Prophet (peace and blessings be upon him) would not have commanded it. However, he commanded it and made it an act of worship by saying: "My Lord commanded me to lengthen my beard and trim my mustache." The people of truth are unanimous that faith is both a statement and an action, some of which is outward and some inward, just as prayer is an action of the limbs and not merely of the heart.