The Kitáb-i-Aqdas - The Most Holy Book
Index term: Sunrise
k17.
These are the ordinances of God that have been set down in the Books and Tablets by His Most Exalted Pen. Hold ye fast unto His statutes and commandments, and be not of those who, following their idle fancies and vain imaginings, have clung to the standards fixed by their own selves, and cast behind their backs the standards laid down by God. Abstain from food and drink from sunrise to sundown, and beware lest desire deprive you of this grace that is appointed in the Book.
k33.
O people of Bahá! It is incumbent upon each one of you to engage in some occupation -- such as a craft, a trade or the like. We have exalted your engagement in such work to the rank of worship of the one true God. Reflect, O people, on the grace and blessings of your Lord, and yield Him thanks at eventide and dawn. Waste not your hours in idleness and sloth, but occupy yourselves with what will profit you and others. Thus hath it been decreed in this Tablet from whose horizon hath shone the day-star of wisdom and utterance. The most despised of men in the sight of God are they who sit and beg. Hold ye fast unto the cord of means and place your trust in God, the Provider of all means.
k115.
Blessed is he who, at the hour of dawn, centring his thoughts on God, occupied with His remembrance, and supplicating His forgiveness, directeth his steps to the Mashriqu'l-Adhkár and, entering therein, seateth himself in silence to listen to the verses of God, the Sovereign, the Mighty, the All-Praised. Say: The Mashriqu'l-Adhkár is each and every building which hath been erected in cities and villages for the celebration of My praise. Such is the name by which it hath been designated before the throne of glory, were ye of those who understand.
n5.
at noon and in the morning and the evening
Regarding the definition of the words "morning", "noon" and "evening", at which times the currently binding medium Obligatory Prayer is to be recited, Bahá'u'lláh has stated that these coincide with "sunrise, noon and sunset" (Q&A 83). He specifies that the "allowable times for Obligatory Prayers are from morning till noon, from noon till sunset, and from sunset till two hours thereafter". Further, 'Abdu'l-Bahá has stated that the morning Obligatory Prayer may be said as early as dawn.
The definition of "noon" as the period "from noon till sunset" applies to the recitation of the short Obligatory Prayer as well as the medium one.
n25.
We have enjoined upon you fasting during a brief period
Fasting and obligatory prayer constitute the two pillars that sustain the revealed Law of God. Bahá'u'lláh in one of His Tablets affirms that He has revealed the laws of obligatory prayer and fasting so that through them the believers may draw nigh unto God.
Shoghi Effendi indicates that the fasting period, which involves complete abstention from food and drink from sunrise till sunset, is

. . . essentially a period of meditation and prayer, of spiritual recuperation, during which the believer must strive to make the necessary readjustments in his inner life, and to refresh and reinvigorate the spiritual forces latent in his soul. Its significance and purpose are, therefore, fundamentally spiritual in character. Fasting is symbolic, and a reminder of abstinence from selfish and carnal desires.

Fasting is enjoined on all the believers once they attain the age of 15 and until they reach the age of 70 years.
A summary of the detailed provisions concerning the law of fasting and of the exemptions granted to certain categories of people is contained in the Synopsis and Codification, section IV.B.1.-6. For a discussion of the exemptions from fasting see notes 14, 20, 30 and 31.
The nineteen-day period of fasting coincides with the Bahá'í month of 'Alá', usually 2-20 March, immediately after the termination of the Intercalary Days (see notes 27 and 147), and is followed by the feast of Naw-Rúz (see note 26).
n32.
Abstain from food and drink from sunrise to sundown
This relates to the period of fasting. In one of His Tablets, 'Abdu'l-Bahá, after stating that fasting consists of abstinence from food and drink, further indicates that smoking is a form of "drink". In Arabic the verb "drink" applies equally to smoking.
n142.
the hour of dawn
With reference to attending dawn prayers in the Mashriqu'l-Adhkár, the Bahá'í House of Worship, Bahá'u'lláh has explained that, although the actual time specified in the Book of God is "the hour of dawn", it is acceptable at any time from "the earliest dawn of day, between dawn and sunrise, or even up to two hours after sunrise" (Q&A 15).
q15.
 
Question: Concerning the remembrance of God in the Mashriqu'l-Adhkár "at the hour of dawn".
Answer: Although the words "at the hour of dawn" are used in the Book of God, it is acceptable to God at the earliest dawn of day, between dawn and sunrise, or even up to two hours after sunrise.
q83.
 
Question: Concerning the definition of "morning", "noon" and "evening".
Answer: These are sunrise, noon and sunset. The allowable times for Obligatory Prayers are from morning till noon, from noon till sunset, and from sunset till two hours thereafter. Authority is in the hand of God, the Bearer of the Two Names.