The Birth of the Mahdī عليه السلام

Saʿd b. ʿAbd Allāh said: “Al-Muʿallā b. Muḥammad al-Baṣrī narrated to us, from Muḥammad b. Jumhūr and another (from Muḥammad b. Abī ʿUmayr) from ʿAbd Allāh b. Sinān, from Abī ʿAbd Allāh عليه السلام. He (ʿAbd Allāh b. Sinān) expressed: “I heard him (Imam al-Ṣādiq) saying: “In regard to the Qāʾim عليه السلام, there is a precedent from Mūsā b. ʿImrān عليه السلام.” I asked: “And what is the precedent from Mūsā b. ʿImrān?,” to which he replied: “The concealment of his birth, and his occultation from his people.” I followed up: “For how many years was Mūsā b. ʿImrān occulted from his family and his people?” He said: “Twenty-eight years.”