80 year prophecy - The prophecy in its various forms

 Below are the places where this prophecy can be found in its different forms:

1. 1865 - Tadkhirah  - Eighty years - a few years less or some years more.

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"Your age will be eighty years—a few years less or some years more; and you will live long enough to witness your distant progeny. - Tadkhirah p9 (direct link to the page)

2. 1891 - Tadkhirah - Eighty years or thereabouts.

"We shall bestow upon you a good life; eighty years or thereabouts." - Tadkhirah p243

3. 1892 - Nishaan-e-Asmani  - Eighty years or thereabout.

"Now, let it be clear, that I was commanded, through a specific revelation, to call the people to Allah, in the fortieth year of my life, and I was given the glad tidings that I will live up to eighty years or thereabout. In view of this revelation, the tenure of my prophetic mission will extend to forty years out of which ten full years have already passed." - The Heavenly sign p28 (Nishaan-e-Asmaani English translation)

Earlier in the book, on p. 14, he writes:

"These verses also indicate that after being commissioned, the reformer will live for forty years, while it is well known that Sayyid Sahib passed away from this transitory world just a few years after his advent. It is evident from Brahin-e-Ahmadiyya that I was commissioned to revive the faith at the age of forty, about eleven years ago. According to the prophecy mentioned in Izala Auham: it appears that the tenure of my mission will extend to forty years. And it is Allah Who knows best." - The Heavenly sign p14

From the above passages we learn:

• Ghulam Ahmad was commissioned as a Mujaddid at age 40.
• At the time of writing the book (1892), he was 10 or 11 years into his career as a Mujaddid. This would mean that he was 50 or 51 years old when writing this book.
• He was a decade into his tenure as Mujaddid, and his tenure was supposed to extend to 40 years. He therefore had another 30 years to live in order to complete his mission.
• His birth year was 1840 or 1841 

Ghulam Ahmad's mission was supposed to extend for another 30 years after writing this book, but he would only live for another 16 years before dying in 1908.

4. 1900 - Tadkhirah - Eighty years or thereabout.

"We shall bestow upon you a pleasant life. Eighty years or thereabout or We shall add some years to it. The promise of Allah is bound to be fulfilled. This is of the mercy of your Lord. He will complete His favour unto you so that it should be a Sign for the believers. Allah will help you in many fields." - Tadkhirah p508

5. 1900 - Tadkhirah - eighty years or a few years less or a few years more.

 

"We shall bestow upon you a pleasant and comfortable life, eighty years or thereabouts—meaning, a few years less or a few years more" - Tadkhirah p529

6. 1902  - A gift for Nadwah - 80 years

"It has been prophesied that I too will be granted approximately 80 years in order to complete my mission." - A gift to an-Nadwah p12 (Tuhfa Nadwah English translation)

7. 1905 - Brahin E Ahmadiyya, Volume 5 - Between 74 and 86.

"the actual words of the Revelation that pertain to this promise, however, fix the age between 74 and 86." - Brahin e Ahmadiyya Part V p347

8. 1906 - Tadkhirah - Eighty years or 4/5 less, or 4/5 more.

" Therefore, your sight is sharp today. Allah will lengthen your days. [Urdu] Eighty years—four or five more, or four or five less." - Tadkhirah p899

The version of this prophecy found in Brahin-e-Ahmadiyya, Volume 5, gives Ghulam Ahmad the largest age range: from 74 to 86.