Hazrat Mahdi (as) will begin communicating the religion in hijri 1400 (1980 ad)

PEOPLE WILL GATHER AROUND HAZRAT MAHDI (AS) IN THE YEAR 1400. (Risalat al-Khuruj al-Mahdi, p. 108) 

This hadith makes it clear that Hijri 1400 will be the year when Hazrat Mahdi (as) begins his work in Istanbul and people first start collecting around him. In addition, Bediuzzaman also states in his works that Hazrat Mahdi (as) will begin communicating the religion in the Hijri year 1400: 

... [THEY] SUPPOSE[D] A FACT [the coming of Hazrat Mahdi (as)] THAT WOULD OCCUR IN THE FUTURE OF THE WORLD ONE THOUSAND FOUR HUNDRED YEARS LATER TO BE CLOSE TO THEIR CENTURY... (Bediuzzaman Said Nursi, Words, 'The Twenty-fourth Word: Third Branch, Eight Principle) 

In addition, Bediuzzaman has aldo revealed that Hazrat Mahdi (as) will begin communicating the word in Hijri 1400: 

COUNT TWO OR THREE DECADES AFTER THE YEAR/DECADE OF HIJRI 1400. AT THAT TIME, HAZRAT MAHDI (AS) EMERGES… (Asmal Masalik Lieyyam Mahdiyy Maliki Li Kull-id Dunya Biemrillah-il Malik, Qalda bin Zayd, p. 216) 

THE WALAYAT (SAINTSHIP) WILL COME TO AN END WITH HAZRAT MAHDI (AS) 

In his work “al-Jawab al-Mustaqim,”written as an answer to questions posed by al-Hakim al-Tirmidhi in his “Hatm’al-awliya,”Muhyiddin Ibn Arabiwrites:

“The age of property will come to an end with him, [Hazrat Mahdi (as)], and walayat will end with him...” (Muhyiddin IbnArabi, al-Jawab al-Mustaqim amma Seele anhu al-Hakim al-Tirmidhi, Bayazid, no: 3750, sheet 242b)