Genesis 25:31, 32, 33

“All right,” Jacob replied, “but trade me your rights as the firstborn son.”

“Look, I’m dying of starvation!” said Esau. “What good is my birthright to me now?”

But Jacob said, “First you must swear that your birthright is mine.” So Esau swore an oath, thereby selling all his rights as the firstborn to his brother, Jacob.