'Harden Your Hearts' in the Bible

do not harden your hearts as they did when they provoked me during the time of testing in the wilderness.

As it is said, "Today, if you hear his voice, do not harden your hearts as they did when they provoked me."

he again fixes a definite day "Today" - saying long afterward through David, as already quoted, "Today, if you hear his voice, do not harden your hearts."