You can only sacrifice a creature you control.
A few sources...
From the quick start guide:
Sometimes a card tells you to
sacrifice a creature or some other permanent.
To sacrifice a permanent, you move it from
the battlefield to your graveyard. You can’t
regenerate it or save it in any way. You can
sacrifice only your own permanents.
From the glossary in the basic rules, page 31:
To choose one of your permanents on the battlefield
and put it into its owner’s graveyard. You can sacrifice
only permanents you control. Sacrificing a permanent
is different from destroying it, so the permanent can’t be
regenerated. You can sacrifice a permanent only if a spell
or ability tells you to, or if it’s part of a cost.
And the comprehensive rule where that comes from:
701.15a To sacrifice a permanent, its controller moves it from the battlefield directly to its owner’s graveyard. A player can’t sacrifice something that isn’t a permanent, or something that’s a permanent he or she doesn’t control. Sacrificing a permanent doesn’t destroy it, so regeneration or other effects that replace destruction can’t affect this action.