What is the exact rule that states a card requires valid target(s) before being played?

Ruling: Rule 562.1 states that you must check that all chosen targets are legal, which establishes the requirement for valid targets when playing a card.

Nuances:

• Rule 723.1.d.1 provides a parallel example for cards played from Hidden, explicitly stating that a card cannot be played without valid targets (similar to cards played from hand)
• Rule 559 covers making necessary choices during card play, which is part of the targeting process