Genesis 25:30-33 New King James Version (NKJV)

30. And Esau said to Jacob, “Please feed me with that same red stew, for I am weary.” Therefore his name was called Edom.

31. But Jacob said, “Sell me your birthright as of this day.”

32. And Esau said, “Look, I am about to die; so what is this birthright to me?”

33. Then Jacob said, “Swear to me as of this day.”So he swore to him, and sold his birthright to Jacob.

Genesis 25