We suspect that the book of John was originally written in Aramaic, and translated into Greek. If so, it would explain this “mystery quote” at John 7:38 that nobody can seem to find.
You see, most Western Bibles are translated from the ancient Greek manuscripts, all of which quote Jesus as saying:
as the Scripture says...
Then it follows with words about waters flowing from someone. Yet nobody can find any scripture with that wording. What’s going on?
Well, (what we belive to be) the original Aramaic actually doesn’t say “Scripture”, but “Scriptures” – yes, the plural.
It seems that the Greek translator(s) simply made a mistake. They didn’t notice that Jesus was not quoting a single verse (as he does many times elsewhere); but this time, he was summarizing what many scriptures say! There are multiple verses in prophecy that speak of water as being like God’s Spirit or the actions of His Spirit (e.g. Isaiah 44:3), water healing (e.g. Isaiah 55:1), and one even states that believers will be like springs of figurative “water” (Isaiah 58:11).
Thus Jesus was not quoting one particular verse, he was referring to a common prophetic symbol in the Bible.