The Kitáb-i-Aqdas - The Most Holy Book
Index term: Birth of Bahá'u'lláh, under Twin Holy Birthdays; Holy Days
Question: Concerning the Festival of the Twin Birthdays.
Answer: The Birth of the Abhá Beauty [Bahá'u'lláh] was at the hour of dawn on the second day of the month of Muharram [first month of the Islamic lunar calendar], the first day of which marketh the Birth of His Herald. These two days are accounted as one in the sight of God.