Some people, such as the Antichrist, allege divinity and people believe in the miracles that appear at their hands while they disbelieve in the miracles that appear at the hands of those who alleged that they are prophets, such as Musaylimah the Liar, while in both cases the claims are false.
Why do people believe the miracles in the first case and disbelieve the miracles in the second?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu 'alyhi wa sallam, is His slave and Messenger.

There is a great difference between the miracles of the prophets, may Allaah exalt their mention, and supernatural phenomena that appear at the hands of liars and swindlers.

No man or Jinn can produce a miracle the same as or even anything like the miracles of the prophets, may Allaah exalt their mention, while the supernatural things that happen at the hands of the liars can be imitated, as stated by Shaykhul-Islam Ibn Taymiyyah when he said, “The miracles that appear at the hands of the prophets cannot be challenged or imitated, contrary to those of other than the prophets - which can be challenged.”

Hence, the supernatural things that occurred at the hands of Musaylimah the Liar could never prove truthfulness on his part; rather, Allaah The Almighty gave him such things to lure him. Such things did not prove his truthfulness in any way regarding his claims of being a prophet, and nothing could have been done to prove his truthfulness because people witnessed his lying and immorality and knew for sure that he was not a prophet, as prophets can never be liars or debauchers.

Shaykhul-Islam Ibn Taymiyyah   said,

The proof of truthfulness entails the truthfulness of the one who claimed it. This is why the signs of truthfulness can never appear at the hands of liars. Some people may counter that there are supernatural things that happen at the hands of those who falsely allege to be prophets while they are liars. Indeed, this only happens in a way that could never prove their truthfulness, as is the case with sorcerers and soothsayers who do supernatural things accompanied by what proves their deceit.

Likewise, the supernatural events that Allaah The Almighty causes to appear at the hands of the Antichrist are intended for trial rather than proving his truthfulness.

Shaykul-Islam Ibn Taymiyyah said, “We see that supernatural events may take place at the hands of the one who alleges that he is God, such as the Antichrist, but this would not prove his truthfulness because he will be an obvious liar in his allegation. We thus say that it will be impossible for him to have any proof of his truthfulness.”

The supernatural things that take place at the hands of the Antichrist would thus be of no value, as they would not prove his truthfulness. This is because his claim will be impossible from the outset, and he will carry many signs that will prove that he is lying.

For example, the word “Kaafir” (disbeliever) will be written between where his eyes should be, and he will be one-eyed, in addition to his inability to kill the person whom he has apparently killed before (and who then comes back to life).

These signs will prove that he is lying and show that the supernatural things that happen at his hands are no proof of his truthfulness. The only purpose behind these supernatural things is to entice the disbelievers and to test the believers.

Finally, Shaykhul-Islam Ibn Taymiyyah   said, “It is impossible for any creature to be God; hence, the occurrence of supernatural events at their hands can never prove the truthfulness of an impossible claim.”

Allaah Knows best.