Aaron's Rod

And when the morning was come, he assembled all Israel, six hundred thousand men, and showed the seals to the princes of the tribes, and opened the tabernacle of witness, and brought forth the rods. And the rod of Aaron was found not only to have blossomed, but to bear fruit upon it.

Numbers 17:8, as St Clement of Rome gives it

For who knows not that a rod, after losing its bark, will never sprout, not even if it be planted in the midst of rivers? But since God is not dependent on the nature of trees, but is the Creator of their natures, the unfruitful, and dry, and barkless rod budded, and blossomed, and bare almonds. He, then, who for the sake of the typical high-priest gave fruit supernaturally to the rod, would He not for the sake of the true High-Priest grant to the Virgin to bear a child?

Cyril of Jerusalem, Catechetical Lectures XII.28