As to thy question concerning interest and profit on gold and silver: Some years ago the following passage was revealed from the heaven of the All-Merciful in honour of the one who beareth the name of God, entitled Zaynu'l-Muqarrabin  -- upon him be the glory of the Most Glorious. He -- exalted be His Word -- saith: Many people stand in need of this. Because if there were no prospect for gaining interest, the affairs of men would suffer collapse or dislocation. One can seldom find a person who would manifest such consideration towards his fellow-man, his countryman or towards his own brother and would show such tender solicitude for him as to be well-disposed to grant him a loan on benevolent terms.  Therefore as a token of favour towards men We have prescribed that interest on money should be treated like other business transactions that are current amongst men. Thus, now that this lucid commandment hath descended from the heaven of the Will of God, it is lawful and proper to charge interest on money, that the people of the world may, in a spirit of amity and fellowship and with joy and gladness, devotedly engage themselves in magnifying the Name of Him Who is the Well-Beloved of all mankind. Verily He ordaineth according to His Own choosing. He hath now made interest on money lawful, even as He had made it unlawful in the past. Within His grasp He holdeth the kingdom of authority. He doeth and ordaineth. He is in truth the Ordainer, the All-Knowing.
[1 One of the early believers who is best known to the friends for his reliable transcriptions of the Tablets of Bahá’u’lláh. (See Memorials of the Faithful pp. 150-153.)]
[2 Such loans as bear no interest and are repayable whenever the borrower pleases.]