Okay, I've been brushing up on my Dictionary definitions.
And the definition seems complicated. And slightly varies from one Dictionary to another.
What I take is that evidence isn't proof, but something that can be used as proof.
But it still leads to the question of, "Proof of what?"
For my part, evidence is closely linked with empiricism and logic. I'll give an example from a deductive categorical syllogism:
Premise 1: All cats in my room are white.
Premise 2: This cat is in my room.
Conclusion: This cat is white.
Notice how, in the example I've given, the premises are sensory perceptions. If you can see the whole room, then you can see all of the cats that are in it and affirm that they are white empirically. This becomes evidence for the conclusion "This cat is white." When paired with Premise 2, it becomes a logical proof that "This cat is white."
The issue with the OP is that it isn't giving premises. A messenger from God would be evidence of the existence of God. Writings from that messenger could be evidence for that messenger's existence.
The issue is that there is an implicit premise here that the writings are actually from a messenger of God, which is just a claim. In other words, it's a conclusion that we do not have the premises to, and thus it is not evidence.
Worse than that, the entire argument is circular. If we could prove that the writings were from a messenger of God, then we would have already proven God. Which means that even the supposed evidence stated earlier isn't actually evidence, either, because it affirms the consequent in the premises.
Affirming the consequent is when your conclusion is the same or implied by one of your premises, such as:
Premise 1: I am immortal.
Premise 2: Immortal beings cannot feel pain.
Conclusion: I am immortal.
It doesn't logically follow, so the premise "Immortal beings cannot feel pain" isn't proper evidence for the claim "I am immortal" in this context.
I hope this helps. I apologize for the length.