There is no specific guidance on such scenario from FTA. However KSA has addressed this matter in one of their guides: https://gazt.gov.sa/en/HelpCenter/guidelines/Documents/VAT_Recreation_and_Entertainment_English.pdf As per this, any discretionary tips (i.e where the customer is under no obligation to provide a tip and has not been provided with any suggested tip amount) then these will not be treated as consideration for services paid to the Restaurant hence should not be subject to VAT. These could be situations where a 'Tips Box' is made available at the counter and money collected is shared between employees or where a restaurant provides any summary document to the customer at end of their meal and they are allowed to enter any 'Tip' amount which is then collected along with invoice and passed on to employees. In either case one would have to retain evidence of these tips passed on to the employees in full.

If the TIP is not compulsory or suggestive action, pure discretion should be of the customer and proper document is available to substantiate that the amount is distributed to waiters, then it should be outside the scope of VAT.