Most of the quotes with leaven are from the Old Testament and in the New Testament warning against the leaven of the Pharisees and Herod.
On the other hand -- Luke 13:20-21 (This is what I always think of.)
- 20
- Again he said, "To what shall I compare the kingdom of God?
- 21
- It is like yeast that a woman took and mixed (in) with three measures of wheat flour until the whole batch of dough was leavened."