The disciples witnessed Thomas' confusion.
James 1:5-6--5If any of you lacks wisdom, you should ask God, who gives generously to all without finding fault, and it will be given to you. 6But when you ask, you must believe and not doubt, because the one who doubts is like a wave of the sea, blown and tossed by the wind.
The disciples witnessed Thomas' confrontation.
Romans 10:9--If you declare with your mouth, "Jesus is Lord," and believe in your heart that God raised him from the dead, you will be saved.
The disciples witnessed Thomas' confession.
Matthew 16:15-16--15He said to them, "But who do you say that I am?" 16Simon Peter replied, "You are the Christ, the Son of he living God."