The Kitáb-i-Aqdas

Many rules about dress had their origins in the laws and traditional practices of the world’s religions. For example, the Shí’ih clergy adopted for themselves a distinctive headdress and robes and, at one time, forbade the people to adopt European attire. Muslim practice, in its desire to emulate the custom of the Prophet, also introduced a number of restrictions with regard to the trim of the moustache and the length of the beard.

Bahá’u’lláh removed such limitations on one’s apparel and beard. He leaves such matters to the “discretion” of the individual, and at the same time calls upon the believers not to transgress the bounds of propriety and to exercise moderation in all that pertains to dress.