It hath been forbidden you to carry arms unless essential, and permitted you to attire yourselves in silk. The Lord hath relieved you, as a bounty on His part, of the restrictions that formerly applied to clothing and to the trim of the beard. He, verily, is the Ordainer, the Omniscient. Let there be naught in your demeanour of which sound and upright minds would disapprove, and make not yourselves the playthings of the ignorant. Well is it with him who hath adorned himself with the vesture of seemly conduct and a praiseworthy character. He is assuredly reckoned with those who aid their Lord through distinctive and outstanding deeds.

The Lord hath relieved you . . . of the restrictions that formerly applied to clothing and to the trim of the beard.
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.