Genesis 27:38

And Esau said unto his father, Hast thou but one blessing, my father? Bless me, even me also, O my father. And Esau lifted up his voice and wept. It is to this scene that Hebrews 12:17 refers, for Esau could not persuade his father to reconsider his decision, although he made the effort with tears. His were in this case not tears of true repentance over his sin, but merely of bitterness over the result of his folly. This fact Isaac now understood.