S4·E3 The Lost Mattress

Mr. Krabs complains that his back hurts, so SpongeBob and Patrick buy a new mattress and Squidward tries to take credit for it. They give the new mattress to Mr. Krabs, but Mr. Krabs put his money in his old mattress, which SpongeBob, Patrick, and Squidward must find while Mr. Krabs is at the hospital.