Book of Jasher 56:64
And he asked, saying, Why do you not bury the dead, and what is this great consternation? and they answered him the words of Esau and his sons; and he ran to Esau in the midst of the battle, and he slew Esau with a sword, and he cut off his head, and it sprang to a distance, and Esau fell amongst the people of the battle.