Knowledge Pool and Curse of Exhaustion on the battlefield.
Curse of Exhaustion attached to an opponent.
Steps
Whenever the opponent with Curse of Exhaustion attached casts a spell from their hand, Knowledge Pool triggers, exiling that spell.
Because Curse of Exhaustion prevents the opponent from casting more than one spell each turn, the opponent cannot cast the spell permitted by Knowledge Pool, or any other spell that turn.
Results
Exile all spells cast from target opponent's hand.