Kitabul Motazar: It is quoted from Hasan bin Sulaiman, student of Shaheed Awwal (r.a.) that he saw in a writing of Imam Hasan Askari (a.s.) as follows:
“A spring of the water of life will burst forth [Mahdi will appear] for them at a time when they would have burnt in the flames of calamities and years equal to the numerical values of Alif Laam Meem, Taa Haa and Taa Seen will have passed.”
[The Promised Mahdi, Allamah Muhammad Baqir al-Majlisi, Biharul Anwar, Volume 13 (Old Edition)/Volumes 51-52-53 (New Edition)]