August 17

…in the beginning the prophethood of Muhammad was concealed, and no one knew of it save Khadíjih and Ibn-i-Nawfal, [1] until it was publicly announced three years later. 
- ‘Abdu’l-Baha  (Table talks in Akka, authenticated by ‘Abdu’l-Baha; ‘Some Answered Questions’ – 2014 revised translation by the Baha’i World Centre)
[1] That is, Muhammad’s wife and her cousin Varaqih-ibn-i-Nawfal.