Twelver Shī‘a believe that al-Mahdī was born in 869 (15 Sha‘bān 255 AH) and assumed Imamate at 5 years of age following the martyrdom of his father Imam Hasan al-Askari. In the early years of his Imamate he would only contact his followers through The Four Deputies. After a 69-year period,[6][7] known as Minor Occultation, a few days before the death of his fourth deputy Abul Hasan Ali ibn Muhammad al-Samarri in 941, he is believed to have sent his followers a letter. In that letter that was transmitted by al-Samarri he declared the beginning of Major Occultation during which Mahdi is not in contact with his followers.