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.

We have decreed that a third part of all fines shall go to the Seat of Justice, and We admonish its men to observe pure justice, that they may expend what is thus accumulated for such purposes as have been enjoined upon them by Him Who is the All-Knowing, the All-Wise. O ye Men of Justice! Be ye, in the realm of God, shepherds unto His sheep and guard them from the ravening wolves that have appeared in disguise, even as ye would guard your own sons. Thus exhorteth you the Counsellor, the Faithful.

Ye have been forbidden in the Book of God to engage in contention and conflict, to strike another, or to commit similar acts whereby hearts and souls may be saddened. A fine of nineteen mithqáls of gold had formerly been prescribed by Him Who is the Lord of all mankind for anyone who was the cause of sadness to another; in this Dispensation, however, He hath absolved you thereof and exhorteth you to show forth righteousness and piety. Such is the commandment which He hath enjoined upon you in this resplendent Tablet. Wish not for others what ye wish not for yourselves; fear God, and be not of the prideful. Ye are all created out of water, and unto dust shall ye return. Reflect upon the end that awaiteth you, and walk not in the ways of the oppressor. Give ear unto the verses of God which He Who is the sacred Lote-Tree reciteth unto you. They are assuredly the infallible balance, established by God, the Lord of this world and the next. Through them the soul of man is caused to wing its flight towards the Dayspring of Revelation, and the heart of every true believer is suffused with light. Such are the laws which God hath enjoined upon you, such His commandments prescribed unto you in His Holy Tablet; obey them with joy and gladness, for this is best for you, did ye but know.

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.

nine mithqáls of gold, to be doubled if they should repeat the offence
A mithqál is a unit of weight. The weight of the traditional mithqál used in the Middle East is equivalent to 24 nakhuds. However, the mithqál used by the Bahá’í­s consists of 19 nakhuds, “in accordance with the specification of the Bayán” (Q&A 23). The weight of nine of these mithqáls equals 32.775 grammes or 1.05374 troy ounces.
In relation to the application of the fine, Bahá’u’lláh clearly specifies that each succeeding fine is double the preceding one (Q&A 23); thus the fine imposed increases in geometrical progression. The imposition of this fine is intended for a future condition of society, at which time the law will be supplemented and applied by the Universal House of Justice.

A fine . . . had formerly been prescribed . . . for anyone who was the cause of sadness to another
Bahá’u’lláh abrogates the law of the Persian Bayán concerning the payment of a fine in reparation for causing sadness to one’s neighbour.

Question: If intercourse take place between a couple during their year of patience, and they become estranged again thereafter, must they recommence their year of patience, or may the days preceding the intercourse be included in the reckoning of the year? And once divorce hath taken place, is it necessary that a further period of waiting be observed?
Answer: Should affection be renewed between the couple during their year of patience, the marriage tie is valid, and what is commanded in the Book of God must be observed; but once the year of patience hath been completed and that which is decreed by God taketh place, a further period of waiting is not required. Sexual intercourse between husband and wife is forbidden during their year of patience, and whoso committeth this act must seek God’s forgiveness, and, as a punishment, render to the House of Justice a fine of nineteen mithqáls of gold.

Question: Concerning the punishment of the adulterer and adulteress.
Answer: Nine mithqáls are payable for the first offence, eighteen for the second, thirty-six for the third, and so on, each succeeding fine being double the preceding. The weight of one mithqál is equivalent to nineteen nakhuds in accordance with the specification of the Bayán.