Evangelize

• WOTC Official Reminder Textofficial rules
  Buyback — You may pay an additional cost as you cast this spell. If you do, put this card into your hand as it resolves.

• WWizards of the Coast2006-09-25
  Official Ruling
  When you put the spell on the stack, you choose an opponent, then that opponent chooses the target. This is not a choice made on resolution.
• WWizards of the Coast2006-09-25
  Official Ruling
  The target of the spell is a creature the chosen opponent controls. As Evangelize resolves, if the target isn’t a creature controlled by the chosen opponent, Evangelize won’t resolve. If Evangelize’s target is changed (via Shunt, for example), the new target must be a creature controlled by the chosen opponent.

Rulings via Scryfall