A good solid prophesy usually has some kind of time measurement associated with it. For example, Jesus predicted that he would rise after three days in the presence of his disciples. "Therefore, when He had risen from the dead, His disciples remembered that He had said this to them; and they believed the Scripture and the word which Jesus had said." (John 2:22)
See? It was that simple. Jesus makes a prophesy with a time measurement in place. The prophesy happens as described. And the disciples now have their proof of Jesus and his word.
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M*W: Well, it didn't happen exactly like that. Jesus wasn't gone for 3 days. The myth goes that he was put on the cross at 3 pm, and was taken down at 6 pm on Friday. He was in the tomb (or wherever) until 6 am Sunday morning. That's a total of only 36 hours... not 3 days. But, then, it's just a myth.