The Kitáb-i-Aqdas
Know thou that polygamy is not permitted under the law of God, for contentment with one wife hath been clearly stipulated. Taking a second wife is made dependent upon equity and justice being upheld between the two wives, under all conditions. However, observance of justice and equity towards two wives is utterly impossible. The fact that bigamy has been made dependent upon an impossible condition is clear proof of its absolute prohibition. Therefore it is not permissible for a man to have more than one wife.
Polygamy is a very ancient practice among the majority of humanity. The introduction of monogamy has been only gradually accomplished by the Manifestations of God. Jesus, for example, did not prohibit polygamy, but abolished divorce except in the case of fornication; Muḥammad limited the number of wives to four, but making plurality of wives contingent on justice, and reintroducing permission for divorce; Bahá’u’lláh, Who was revealing His Teachings in the milieu of a Muslim society, introduced the question of monogamy gradually in accordance with the principles of wisdom and the progressive unfoldment of His purpose. The fact that He left His followers with an infallible Interpreter of His Writings enabled Him to outwardly permit two wives in the Kitáb-i-Aqdas but uphold a condition that enabled ‘Abdu’l-Bahá to elucidate later that the intention of the law was to enforce monogamy.
90.he who would take into his service a maid may do so with propriety ¶63
Bahá’u’lláh states that a man may employ a maiden for domestic service. This was not permissible under Shí‘íh Muslim practice unless the employer entered into a marriage contract with her. Bahá’u’lláh emphasizes that the “service” referred to in this verse is solely “such as is performed by any other class of servants, be they young or old, in exchange for wages” (Q and A 30). An employer has no sexual rights over his