The Kitáb-i-Aqdas

Marriage with one’s stepmother is here explicitly prohibited. This prohibition also applies to marrying one’s stepfather. Where Bahá’u’lláh has expressed a law between a man and a woman it applies mutatis mutandis as between a woman and a man unless the context should make this impossible.

‘Abdu’l-Bahá and Shoghi Effendi confirmed that, while stepmothers are the only category of relatives mentioned in the text, this does not mean that all other unions within a family are permissible. Bahá’u’lláh states that it devolves upon the House of Justice to legislate “concerning the legitimacy or otherwise of marrying one’s relatives” (Q and A 50). ‘Abdu’l-Bahá has written that the more distant the blood-relationship between the couple the 223 better, since such marriages provide the basis for the physical well-being of humanity and are conducive to fellowship among mankind.