August 15

Exemption from obligatory prayer and fasting is granted to women who are menstruating; they should, instead, perform their ablutions and repeat 95 times a day between one noon and the next, the verse “Glorified be God, the Lord of Splendour and Beauty”. This provision has its antecedent in the Arabic Bayán, where a similar dispensation was granted.

In some earlier religious Dispensations, women in their courses were considered ritually unclean and were forbidden to observe the duties of prayer and fasting. The concept of ritual uncleanness has been abolished by Bahá’u’lláh.

The Universal House of Justice has clarified that the provisions in the Kitáb-i-Aqdas granting exemptions from certain duties and responsibilities are, as the word indicates, exemptions and not prohibitions. Any believer is, therefore, free to avail himself or herself of an applicable exemption if he or she so wishes. However, the House of Justice counsels that, in deciding whether to do so or not, the believer should use wisdom and realize that Bahá’u’lláh has granted these exemptions for good reason. 
The Universal House of Justice  (The ‘Notes’ section of ‘The Kitab-i-Aqdas’)