In truth, I say that obligatory prayer and fasting occupy an exalted station in the sight of God. It is, however, in a state of health that their virtue can be realized. In time of ill-health it is not permissible to observe these obligations; such hath been the bidding of the Lord, exalted be His glory, at all times. Blessed be such men and women as pay heed, and observe His precepts. All praise be unto God, He who hath sent down the verses and is the Revealer of undoubted proofs!
(Bahá’u’lláh, The Kitáb-i-Aqdas, p. 134)
Some people lay stress on fasting. They affirm that in augmenting the weakness of the body they develop a spiritual sensibility and thus they think to approach God. Weakening one’s self physically does not necessarily contribute to spiritual progress. Humility, kindness, resignation, and all these spiritual attributes emanating from great physical strength are acceptable to God. That an enfeebled man cannot fight is not accounted a virtue. Were physical weakness a virtue the dead would be perfect, for they can do nothing. If a man be just, kind, humble and merciful and his qualities are acquired through the will-power—this is Godlike. A child cannot kill a man; but a Bonaparte can abstain from war, from shedding blood, from devastating countries. A dumb person will not speak ill of any one, a paralyzed hand cannot strike; but a strong arm can refrain from striking. Justice, love and kindness must be the instruments of strength, not of weakness. Exaggerated fasting destroys the divine forces.
(‘Abdu’l-Bahá, Divine Philosophy, p. 98-99)
The law of the Fast is ordained for those who are sound and healthy; as to those who are ill or debilitated, this law hath never been nor is now applicable.
(Bahá’u’lláh, The Importance of Obligatory Prayer and Fasting)