Nineteen-Day Fast to be the one foretold by the Báb, accepted the fast, but altered many of its details and regulations. The Bahá'í fast resembles fasting practices of several other religions. Lent is a period of fasting for Christians, Yom Kippur and many other holidays for Jews, and the fast of Ramadan is practiced by Muslims. The Bahá'í fasting most resembles the fast of Ramadan, except that the period of fasting is defined as a fixed Bahá'í month, whereas Muslims fast during a lunar month, whose specific Gregorian dates vary from year to year. Bahá'u'lláh established the guidelines of the fast in
Fast of the Firstborn of the fast. Additionally, this fast differs from most other fasts established in the Jewish calendar in that this fast is not indicated in the Hebrew Scriptures. This lessens the severity of the fast, and someone who experiences significant discomfort as a result of fasting may break his fast ("Mishnah Berurah" based on the "Rema"). The custom of the Fast of the Firstborn is today observed nearly universally throughout Orthodox Ashkenazic communities. However some Sefardic and Mizrahi communities have not fully adopted the custom. It is not traditionally observed by Yemenite Jews and its practice was discouraged by the former