Some Ans. Questions 1908 by -'Abdu'l-Bahá- 1 Para

The beginning of this lunar reckoning is from the day of the proclamation of the prophethood of Muhammad in the country of Hijaz; and that was three years after His mission, because in the beginning the prophethood of Muhammad was kept secret, and no one knew it save Khadijah and Ibn Nawfal. I After three years it was announced. And Baha'u'llah, in the year 1290 from the proclamation of the mission of Muhammad, caused His manifestation to be known (43:5)

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