Where does “ἐκεῖθεν” come from?

ἐκεῖθεν (Ancient Greek) comes from Ancient Greek ἐκεῖ, from Ancient Greek ἐκεῖνος, from Ancient Greek ἐ-, from Proto-Indo-European h₁e-.

ἐκεῖθεν (Ancient Greek): from that place, thence; thence, from that place;...