Romans 9:18

This is a proof that wherever He chooses He shows mercy, and wherever he chooses He hardens the heart.

Romans 9:22-23

And what if God, while choosing to make manifest the terrors of His anger and to show what is possible with Him, has yet borne with long-forbearing patience with the subjects of His anger who stand ready for destruction,

Treasury of Scripture Knowledge

Summary

For it was of the LORD to harden their hearts, that they should come against Israel in battle, that he might destroy them utterly, and that they might have no favour, but that he might destroy them, as the LORD commanded Moses.

It was

Bible References

It was

Romans 9:18
This is a proof that wherever He chooses He shows mercy, and wherever he chooses He hardens the heart.