Daniel 2:41, 43

In that you saw the feet and toes, partly of potter’s clay and partly of iron, it will be a divided kingdom; but it will have in it the toughness of iron, inasmuch as you saw the iron mixed with common clay.

And in that you saw the iron mixed with common clay, they will combine with one another in the seed of men; but they will not adhere to one another, even as iron does not combine with pottery.