When we think of Prophets, then we think about the miracles they perform. But these days with the technology available, would we believe a miracle, even if we saw it? Still it is one of the criteria, as the Holy Qur'an states:
Say, 'if Mankind and Jinn should gather together to produce the like of this Qur'an, they could not produce the like thereof, even though they should help one another'
The Holy Bible states:
Jesus saith unto her, said I not unto thee, that, if thou wouldest believe, Thou shouldest see the glory of God? Then they took away the stone from the place where the dead was laid. And Jesus lifted up his eyes, and said, ‘father, I thank thee that thou hast heard me. And I know that thou hearest me always, But because of the people which stand by I said it, That they may believe that thou hast sent me.’ And when he thus had spoken, he cried with a loud voice, ‘Lazarus, come forth’ and he that was dead came forth.
Holy Bible, John Chapter 40, verse 44
Hadhrat Mirza Ghulam Ahmad, may peace be upon him, did perform miracles, for instance, there was a student called Abdul Karim, who contracted rabies. In those days there was no cure for rabies, no antibiotics etc, so the doctors gave up. Hadhrat Mirza Ghulam Ahmad, may peace be upon him, prayed and the person was cured. There are many more, like learning 40,000 Arabic root words in a single night, etc. but with miracles, we can have doubt now due to the T.V. and other technology. The greatest sign supporting him was, as we have already mentioned, the Heavenly Sign, a miracle beyond doubt, just like the Holy Qur'an or the miracles of Moses etc. For the Promised Messiah & Mahdi the Heavenly sign was the sign of the eclipse.