In 1897, a Shia scholar called Sheikh Najafi wrote to Mirza Ghulam Ahmad (AS) and challenged him. He claimed that he can show a sign of his truthfulness within 40 minutes, The Promised Messiah (AS) wrote to him and gave him respite. He (AS) told him to show this sign, not in 40 minutes but 40 hours, or even 40 days. Mirza Ghulam Ahmad (AS) challenged that he cannot show such a sign in this time period, and if he shows one, then he is on falsehood.

Within 35 days of this, on 6th March 1897, Allah showed the magnificent sign of the death of Lekh Ram which was the prophecy of the Promised Messiah (AS). Read more about this prophecy here.

February 1st, 1897

This is the reply of the Promised Messiah (AS).

Hadrat [Haji Sheikh Muhammad Rada Tehrani, Najafi, alias] Sheikhul-Islam [who is a Shia] promised in his letter that he was ready to show a Sign within forty minutes. Well then let him announce a prophecy and we shall give him, not forty minutes, but forty hours. Thereafter if no Sign appears on our side within forty days and he shows a Sign within forty hours, or, indeed within forty days, we shall believe in his spiritual eminence and we shall give up our own claim. But if within the period specified a Sign appears on my side and none appears from his side, this would be the proof of my righteousness and of his falsehood.

[Majmu‘a-e-Ishtiharat, vol. 2, p. 198, footnote]
[Tadhkirah, p. 381]

March 10th, 1897

On March 6th, 1897, the sign of the death of Lekh Ram was witnessed by millions of people. As per his challenge, Mirza Ghulam Ahmad (AS) wrote to Sheikh Najafi after 40 days.

Shiekh Najafi had in his letter promised to show a Sign within forty minutes and in my announcement of February 1, 1897, I promised a Sign within forty days…. It is God’s bounty that after thirty five days from February 1, 1897, that is to say within forty days, the Sign of the death of Lekhram Peshawari occurred…. Now on our side the Sign has appeared and Najafi’s falsehood has been established. Even so, to make things easier for him, we are quite willing that as he claimed he should ascend to one of the minarets of the Shahi Masjid [Royal Mosque] in Lahore and throw himself down from it. While Sheikh Najadi [the Satan] has been granted respite**, there would be a sudden end to Shiekh Najafi. If he still does not [come forward to] show his Sign, then: لعنت اللہ الا لکازبین المنافقین [curse of Allah be on the liars.]

[Majmu‘a-e-Ishtiharat, vol. 2, p. 339]
[Tadhkirah, p. 381]

Conclusion

This is yet another simple and profound challenge of Ahmad (AS). These events continue to show the defeat of the entire world against the Messiah sent by Allah. It shows the continuous victory of Mirza Ghulam Ahmad (AS) through the constant support of God Almighty.