From the Baha’i Prayerbook:
The Kitáb-i-Aqdas states: “We have commanded you to pray and fast from the beginning of maturity [15 years]; this is ordained by God, your Lord and the Lord of your forefathers… The traveler, the ailing, those who are with child or giving suck, are not bound by the fast… Abstain from food and drink from sunrise to sundown, and beware lest desire deprive you of this grace that is appointed in the Book.”
The period of the Fast is March 2 through March 20.
This is, O my God, the first of the days on which Thou hast bidden Thy loved ones to observe the Fast. I ask of Thee by Thy Self and by him who hath fasted out of love for Thee and for Thy good-pleasure—and not out of self and desire, nor out of fear of Thy wrath—and by Thy most excellent names and august attributes, to purify Thy servants from the love of aught except Thee and to draw them nigh unto the Dawning-Place of the lights of Thy countenance and the Seat of the throne of Thy oneness. Illumine their hearts, O my God, with the light of Thy knowledge and brighten their faces with the rays of the Daystar that shineth from the horizon of Thy Will. Potent art Thou to do what pleaseth Thee. No God is there but Thee, the All-Glorious, Whose help is implored by all men.
Assist them, O my God, to render Thee victorious and to exalt Thy Word. Suffer them, then, to become as hands of Thy Cause amongst Thy servants, and make them to be revealers of Thy religion and Thy signs amongst mankind, in such wise that the whole world may be filled with Thy remembrance and praise and with Thy proofs and evidences. Thou art, verily, the All-Bounteous, the Most Exalted, the Powerful, the Mighty, and the Merciful.