As for thy mention of the Obligatory Prayer: in truth, anyone who readeth this with absolute sincerity will attract all created things, and confer new life upon the world of being. This servant beseecheth his Lord to assist His loved ones in that which will deliver them from this world’s vicissitudes, its preoccupations, its frustrations, and its darkness, and will adorn them with that which shall under all conditions draw them nigh unto Him. He, verily, is the All-Possessing, the Most High.3
(Bahá’u’lláh, from a Tablet—translated from the Arabic and the Persian) 
The obligatory prayers are binding inasmuch as they are conducive to humility and submissiveness, to setting one’s face towards God and expressing devotion to Him. Through such prayer man holdeth communion with God, seeketh to draw near unto Him, converseth with the true Beloved of his heart, and attaineth spiritual stations.
(‘Abdu’l-Bahá, from a Tablet—translated from the Persian) 
Know thou that in every word and movement of the obligatory prayer there are allusions, mysteries and a wisdom that man is unable to comprehend, and letters and scrolls cannot contain.
(‘Abdu’l-Bahá, from a Tablet—translated from the Arabic) 
In regard to the question which you have been asked by the London Assembly to submit to the Guardian concerning the recital of “Munájáts”:4 He wishes me first to draw your attention to the fact that there is a fundamental difference between “Namáz” and “Munáját”. While the former, being specifically ordained by Bahá’u’lláh, is obligatory and must, in accordance with His definite instructions given in the Aqdas, be recited privately, the latter is neither compulsory nor is there any prescribed way for its recital. But although the friends are thus left free to follow their own inclination when reading the “Munáját” they should take the utmost care that any manner they practise should not acquire too rigid a character, and thus develop into an institution.
This is a point which the friends should always bear in mind, lest they deviate from the clear path indicated by the Teachings.
(From a letter dated 25 October 1934 written on behalf of Shoghi Effendi to an individual believer) 
... the obligatory prayers are by their very nature of greater effectiveness and are endowed with a greater power than the non-obligatory ones, and as such are essential.
(From a letter dated 4 January 1936 written on behalf of Shoghi Effendi to an individual believer) 
The instructions that accompany these prayers, such as the washing of hands and face, of bowing down and of raising one’s hands, have been definitely ordained by Bahá’u’lláh, and as such should be entirely and confidently carried out by the believers, and particularly by the Bahá’í youth, on whose shoulders has been laid the chief responsibility of vindicating the truth and preserving the integrity of the laws and ordinances of the Faith.
The daily obligatory prayers are three in number. The shortest one consists of a single verse which has to be recited once every twenty-four hours and at midday. The medium, which begins with the words, “The Lord is witness that there is none other God but He,” has to be recited three times a day, in the morning, at noon and in the evening. This prayer is accompanied by certain physical acts and gestures. The long prayer, which is the most elaborate of the three, has to be recited only once in every twenty-four hours, and at any time one feels inclined to do so.
The believer is entirely free to choose any one of these three prayers, but is under the obligation of reciting one of them, and in accordance with any specific directions with which it may be accompanied.
(From a letter dated 10 January 1936 written on behalf of Shoghi Effendi to the National Spiritual Assembly of the United States and Canada) 
You had asked about performing obligatory prayers in the Mashriqu’l-Adhkár. He told me to write: “Obligatory prayer is not forbidden in the Mashriqu’l-Adhkár, but the friends have not been and are not required to perform it in the Temple. Congregational prayer is prohibited, save in the Prayer for the Dead. Designating the place and determining the conditions for the recital of obligatory prayers in the Mashriqu’l-Adhkár are secondary matters to be referred to the Spiritual Assembly of that city.”
(From a letter dated 30 January 1937 written on behalf of Shoghi Effendi to an individual believer) 
The Guardian particularly appreciates the fact that you have been faithfully observing Bahá’u’lláh’s injunction regarding the recital of the daily obligatory prayers, and have thereby set such a high example before your Bahá’í fellow-youth. These daily prayers have been endowed with a special potency which only those who regularly recite them can adequately appreciate. The friends should therefore endeavour to make daily use of these prayers, whatever the peculiar circumstances and conditions of their life.
(From a letter dated 23 February 1939 written on behalf of Shoghi Effendi to individual believers) 
With reference to your question regarding the three daily obligatory prayers: the Bahá’í worshipper is not required to recite them all each day, but has to choose one, and should also strictly conform to any instructions revealed by Bahá’u’lláh in connection with its recital, such as the raising of hands, various genuflexions, etc. Those who for some reason or other, especially when physically unable to observe these regulations owing to illness or some bodily defect, cannot conform to these instructions should preferably choose the short prayer, which is exceedingly simple.
(From a letter dated 7 December 1939 written on behalf of Shoghi Effendi to an individual believer) 
He would advise you to only use the short midday Obligatory Prayer. This has no genuflections and only requires that when saying it the believer turn his face towards ‘Akká where Bahá’u’lláh is buried. This is a physical symbol of an inner reality, just as the plant stretches out to the sunlight—from which it receives life and growth—so we turn our hearts to the Manifestation of God, Bahá’u’lláh, when we pray; and we turn our faces, during this short prayer, to where His dust lies on this earth as a symbol of the inner act.
Bahá’u’lláh has reduced all ritual and form to an absolute minimum in His Faith. The few forms that there are—like those associated with the two longer obligatory daily prayers—are only symbols of the inner attitude. There is a wisdom in them, and a great blessing, but we cannot force ourselves to understand or feel these things, that is why He gave us also the very short and simple prayer, for those who did not feel the desire to perform the acts associated with the other two.
(From a letter dated 24 June 1949 written on behalf of Shoghi Effendi to an individual believer) 
As regards the questions about the proper use of the Long Obligatory Prayer: All the writings of the Faith may be read and should be read for the instruction and inspiration of the friends. This includes the specific prayers. If a believer is physically incapable of performing the genuflexions accompanying one of the prayers, and yet he longs to say it as an obligatory prayer, then he may do so. By physically incapable is meant a real physical incapacity which a physician would attest as genuine.
(From a letter dated 17 February 1955 written on behalf of Shoghi Effendi to the Local Spiritual Assembly of Los Angeles, California) 
We have determined, therefore, that it is imperative for all the believers to deepen their awareness of the blessings conferred by the laws which directly foster the devotional life of the individual and, thus, of the community. The essentials of these laws are known to all Bahá’ís, but acquiring greater insight into their significance must include carrying out all the divinely revealed aspects of their observance. These are the laws which pertain to obligatory prayer, fasting and recitation of the Greatest Name ninety-five times a day.
Bahá’u’lláh asserts: “One who performeth neither good deeds nor acts of worship is like unto a tree which beareth no fruit, and an action which leaveth no trace. Whosoever experienceth the holy ecstasy of worship will refuse to barter such an act or any praise of God for all that existeth in the world. Fasting and obligatory prayer are as two wings to man’s life. Blessed be the one who soareth with their aid in the heaven of the love of God, the Lord of all worlds.”
(The Universal House of Justice, from a letter dated 28 December 1999 to the Bahá’ís of the World)