John 9:3 KJV
Jesus answered, Neither hath this man sinned, nor his parents: but that the works of God should be made manifest in him.
Here is one of those passages that illustrate the importance of reading the Bible normally as well as literally. The context of the whole Bible adds depth and accuracy to the passage.
We know that all have sinned and come short of the glory of God. That is as true of this man, and his parents, as it is of every human ever born, excepting, of course, Jesus. This passage should not be read to mean that these three had never sinned. It should be interpreted normally and not too literally, which means we apply the rest of Scripture and know that they have sinned but their sins are not the cause of the son's blindness.
We also see an illustration in this passage of teaching line upon line and precept upon precept, not trying to teach every truth in one lesson. Jesus dealt with the question at hand. He did not spend inordinate amounts of time laying lots or background and giving disclaimers; he simply answered the question and left it up to His audience to know that there was more truth involved in the passage than He took the time to address. He did not begin by saying something like, "Technically all of them have sinned because all are sinners." He did not get sidetracked with doctrines that were peripheral to the topic. He stayed on task. He did not lie in doing so. He did not teach half-truth in doing so. He taught the truth that was pertinent to the question.