Genesis 25:31-34

31 Jacob replied, “First sell me your birthright.”

32 “Look, I am about to die,” Esau said. “What good is the birthright to me?”

33 But Jacob said, “Swear to me first.” So he swore an oath to him, selling his birthright to Jacob.

34 Then Jacob gave Esau some bread and some lentil stew. He ate and drank, and then got up and left.
So Esau despised his birthright.