One of the twelve disciples, Thomas (called the Twin), was not with them when Jesus came.
So the other disciples told him, "We have seen the Lord!" Thomas said to them, "Unless I see the scars of the nails in his hands and put my finger on those scars and my hand in his side, I will not believe."
A week later the disciples were together again indoors, and Thomas was with them. The doors were locked, but Jesus came and stood among them and said, "Peace be with you."
Then he said to Thomas, "Put your finger here, and look at my hands; then reach out your hand and put it in my side. Stop your doubting, and believe!"
Thomas answered him, "My Lord and my God!"
Jesus said to him, "Do you believe because you see me? How happy are those who believe without seeing me!"
In his disciples' presence Jesus performed many other miracles which are not written down in this book.
But these have been written in order that you may believe that Jesus is the Messiah, the Son of God, and that through your faith in him you may have life.
References for John 20:31