Which Scripture is Christ speaking of? Where in the Old Testament did it ever mention a believer, out of his innermost self would have rivers of living water flowing? The answer is no single Scripture, but the Lord Jesus Christ here is speaking generally of quite a number of Scriptures which use this figure and add up together to this sense. He has in mind passages like Isaiah 44:3; 55:1; 58:11. It would perhaps be easier for us if we said as the Scriptures (plural) say. The great figures of water in the Old Testament are pointing exactly to this. And the Lord Jesus Christ rests his statement upon them. Yet none of them mention a belly. Why use this word? Because it is the part of us that craves satisfaction. Instead of craving you will have a source of satisfaction within you. From you will flow benefit and blessing to other people. The greedy becomes generous; the self-seeking becomes out going.