Daniel 2:43
Just as you saw iron mixed with clay, so they will mix themselves with human offspring. Furthermore, they won't remain together, just as iron doesn't mix with clay.
Treasury of Scripture Knowledge
Summary
And whereas thou sawest iron mixed with miry clay, they shall mingle themselves with the seed of men: but they shall not cleave one to another, even as iron is not mixed with clay.
General references
Bible References
General references
Daniel 2:33
its legs made of iron, and its feet made partly of iron and partly of clay.