3 verses have
back
in Edition Clear Qur'an by Talal Itani / Al-Anfaal (The Spoils of War)

8:15O you who believe! When you meet those who disbelieve on the march, never turn your backs on them.

8:16Anyone who turns his back on them on that Day, except while maneuvering for battle, or to join another group, has incurred wrath from God, and his abode is Hell—what a miserable destination!

8:50If only you could see, as the angels take away those who disbelieve, striking their faces and their backs: “Taste the agony of the Burning.”