15. God hath granted you leave to prostrate yourselves on any surface that is clean, for We have removed in this regard the limitation that had been laid down in the Book [# 10]
The requirements of prayer in previous Dispensations have often included prostration. In the Arabic Bayán the Báb called upon the believers to lay their foreheads on surfaces of crystal when prostrating. Similarly, in Islám, certain restrictions are imposed with regard to the surface on which Muslims are permitted to prostrate. Bahá’u’lláh abrogates such restrictions and simply specifies "any surface that is clean".
16. Let him that findeth no water for ablution repeat five times the words "In the Name of God, the Most Pure, the Most Pure", and then proceed to his devotions. [#10]
Ablutions are to be performed by the believer in preparation for the offering of obligatory prayer. They consist of washing the hands and face. If water is unavailable, the repetition five times of the specifically revealed verse is prescribed. See note 34 for a general discussion of ablutions.
Antecedents in earlier Dispensations for the provision of substitute procedures to be followed when no water is available are found in the Qur’án and in the Arabic Bayán.
17. In regions where the days and nights grow long, let times of prayer be gauged by clocks and other instruments that mark the passage of the hours. [#10]
This refers to territories situated in the extreme north or south, where the duration of days and nights varies markedly (Q and A 64 and 103). This provision applies also to fasting.