I can't find anything in the state codes or regs about an employer having to provide a certain amount of hours to an employee. I heard an employee has to pay for at least a 3 hour shift, even if the employee is not need for the 3 full hours. Is this true?

No state requires you be scheduled for a certain number of hours. Some may have laws about how many hours you must be paid for if you are called in or sent home early (that s rare).

No, it is not true, which is why you are not finding it.

While a few states have such a provision, Washington is not one of them.