What is the scripture passage Jesus is referring to? The exact phrase cannot be found in the Hebrew books we have, nor the Greek Septuagint.
So what happened?
- Jesus was summarizing several scriptural ideas
- That particular phrase has been lost or mis-copied to not match exactly
The scriptural support for Jesus' quote is somewhat overwhelming. The references from Matthew Henry alone are: Isaiah 12:3, Exodus 17:6, John 4:14, Jeremiah 2:13, Proverbs 4:23, 1 John 5:10, Proverbs 10:11, Proverbs 5:15-16, Proverbs 1:23, Joel 2:28, Isaiah 44:3, Zechariah 12:10, Isaiah 58:11, (Song of Solomon 4:15 compare John 4:15), Ezekiel 47:1, Zechariah 14:8.
Let's look at a couple. Isaiah 12:3 "Therefore with joy shall ye draw water out of the wells of salvation." That's pretty close, but the edit distance is probably too far for a mis-copy. Another close one is Ezekiel 47:1b "behold, waters issued out from under the threshold of the house eastward". This is in a description of the new temple. Clearly a reference to how all Christians are now temples of God.
There is also Exodus 17:6b "thou shalt smite the rock, and there shall come water out of it, that the people may drink." The rock in this case is a shadow for Jesus Christ. The interesting thing here is that Jesus is telling us the river will be inside of us, shedding light on the coming of the Holy Spirit. (Compare Numbers 20:8, where we are told to "speak to the rock")
Given this brief overview, it would appear that Jesus was exegeting scripture for us. This is not entirely unheard of. There are cases where Jesus expanded on the meaning of scripture over what was commonly held at the time (passages on divorce, the resurrection, etc.).