Time Elemental

When Time Elemental attacks or blocks, at end of combat, sacrifice it and it deals 5 damage to you.
{2}{U}{U}, {T}: Return target permanent that isn't enchanted to its owner's hand.

Masters Edition

Fifth Edition

If Time Elemental attacks or blocks, it deals 5 damage to you and is buried at end of combat.
o2o
Uo
U, oc
T: Return target permanent with no enchantments on it to owner's hand.

Renaissance

Fourth Edition Foreign Black Border

Fourth Edition

o2o
Uo
U, oc
T: Return target permanent to owner's hand. You cannot use this ability on permanents with enchantment cards played on them. If Time Elemental blocks or attacks, destroy it at end of combat. In this case, Time Elemental deals 5 damage to its controller.

You both sacrifice it and deal the 5 damage at end of combat.

A “permanent that isn’t enchanted” is a permanent with no Auras on it.

If Time Elemental attacks or blocks, but you no longer control it at end of combat, you can’t sacrifice it. However, it will still deal 5 damage to you.