The Kitáb-i-Aqdas - The Most Holy Book
Index term: medium, under Obligatory Prayer(s)
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.
n34.
Perform ye . . . ablutions for the Obligatory Prayer
Ablutions are specifically associated with certain prayers. They must precede the offering of the three Obligatory Prayers, the daily recitation of "Alláh-u-Abhá" ninety-five times, and the recital of the verse prescribed as an alternative to obligatory prayer and fasting for women in their courses (see note 20).
The prescribed ablutions consist of washing the hands and the face in preparation for prayer. In the case of the medium Obligatory Prayer, this is accompanied by the recitation of certain verses (see Some Texts Revealed by Bahá'u'lláh Supplementary to the Kitáb-i-Aqdas).
That ablutions have a significance beyond washing may be seen from the fact that even should one have bathed oneself immediately before reciting the Obligatory Prayer, it would still be necessary to perform ablutions (Q&A 18).
When no water is available for ablutions, a prescribed verse is to be repeated five times (see note 16), and this provision is extended to those for whom the use of water would be physically harmful (Q&A 51).
The detailed provisions of the law concerning ablutions are set out in the Synopsis and Codification, section IV.A.10.a.-g., as well as in Questions and Answers numbers 51, 62, 66, 77 and 86.
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.
q86.
 
Question: At noon, which is the time for two of the Obligatory Prayers -- the short midday prayer, and the prayer to be offered in the morning, noon, and evening -- is it necessary in this case to perform two ablutions or would one suffice?
Answer: The renewal of ablutions is unnecessary.