The Kitáb-i-Aqdas - The Most Holy Book
Index term: consequences, under unlawful; Sexual acts
k49.
God hath imposed a fine on every adulterer and adulteress, to be paid to the House of Justice: nine mithqáls of gold, to be doubled if they should repeat the offence. Such is the penalty which He Who is the Lord of Names hath assigned them in this world; and in the world to come He hath ordained for them a humiliating torment. Should anyone be afflicted by a sin, it behoveth him to repent thereof and return unto his Lord. He, verily, granteth forgiveness unto whomsoever He willeth, and none may question that which it pleaseth Him to ordain. He is, in truth, the Ever-Forgiving, the Almighty, the All-Praised.
n36.
or adultery
The Arabic word "ziná", here translated as "adultery", signifies both fornication and adultery. It applies not only to sexual relations between a married person and someone who is not his or her spouse, but also to extramarital sexual intercourse in general. One form of "ziná" is rape. The only penalty prescribed by Bahá'u'lláh is for those who commit fornication (see note 77); penalties for other kinds of sexual offence are left to the Universal House of Justice to determine.
n77.
God hath imposed a fine on every adulterer and adulteress, to be paid to the House of Justice
Although the term translated here as adultery refers, in its broadest sense, to unlawful sexual intercourse between either married or unmarried individuals (see note 36 for a definition of the term), 'Abdu'l-Bahá has specified that the punishment here prescribed is for sexual intercourse between persons who are unmarried. He indicates that it remains for the Universal House of Justice to determine the penalty for adultery committed by a married individual. (See also Q&A 49.)
In one of His Tablets, 'Abdu'l-Bahá refers to some of the spiritual and social implications of the violation of the laws of morality and, concerning the penalty here described, He indicates that the aim of this law is to make clear to all that such an action is shameful in the eyes of God and that, in the event that the offence can be established and the fine imposed, the principal purpose is the exposure of the offenders -- that they are shamed and disgraced in the eyes of society. He affirms that such exposure is in itself the greatest punishment.
The House of Justice referred to in this verse is presumably the Local House of Justice, currently known as the Local Spiritual Assembly.
n134.
the subject of boys
The word translated here as "boys" has, in this context, in the Arabic original, the implication of paederasty. Shoghi Effendi has interpreted this reference as a prohibition on all homosexual relations.
The Bahá'í teachings on sexual morality centre on marriage and the family as the bedrock of the whole structure of human society and are designed to protect and strengthen that divine institution. Bahá'í law thus restricts permissible sexual intercourse to that between a man and the woman to whom he is married.
In a letter written on behalf of Shoghi Effendi it is stated:

No matter how devoted and fine the love may be between people of the same sex, to let it find expression in sexual acts is wrong. To say that it is ideal is no excuse. Immorality of every sort is really forbidden by Bahá'u'lláh, and homosexual relationships He looks upon as such, besides being against nature. To be afflicted this way is a great burden to a conscientious soul. But through the advice and help of doctors, through a strong and determined effort, and through prayer, a soul can overcome this handicap.

Bahá'u'lláh makes provision for the Universal House of Justice to determine, according to the degree of the offence, penalties for adultery and sodomy (Q&A 49).