Isaiah 48:4

4 For I knew how stubborn you were; your neck muscles were iron, your forehead was bronze.

Read Isaiah 48:4 Using Other Translations

Because I knew that thou art obstinate, and thy neck is an iron sinew, and thy brow brass;
Because I know that you are obstinate, and your neck is an iron sinew and your forehead brass,
For I know how stubborn and obstinate you are. Your necks are as unbending as iron. Your heads are as hard as bronze.