'Do Not Harden Your Hearts' in the Bible

do not harden your hearts as in the rebellion, according to the day of the trial in the wilderness,

while it is said, Today if ye will hear his voice, do not harden your hearts as in the rebellion.

again he appoints a certain day, Today, saying in David after so long a time (as it is said), Today if ye will hear his voice, do not harden your hearts.