Bahá’u’lláh designated a nineteen-day fast period each year during which adult Bahá’ís fast from sunrise to sunset each day. This period coincides with the Bahá’í month of Alá—meaning Loftiness—from 2 to 20 March, which immediately precedes the Bahá’í new year. It is a time of prayer, meditation, and spiritual rejuvenation.
Sourced from https://www.bahai.org/beliefs/life-spirit/devotion/fasting