Hebrews 3:15
              While it is said, To day if ye will hear his voice, harden not your hearts, as in the provocation. 
           
                
              Hebrews 4:7
              Again, he limiteth a certain day, saying in David, To day, after so long a time; as it is said, To day if ye will hear his voice, harden not your hearts. 
           
                
              Hebrews 12:26
              Whose voice then shook the earth: but now he hath promised, saying, Yet once more I shake not the earth only, but also heaven.