What is the ruling on purchasing from open buffet restaurants where the buyer pays a certain amount and eats an unknown quantity of food, and is this considered among gharar (uncertainty) transactions?

The Prophet, peace and blessings be upon him, forbade transactions involving gharar (definition), which is that which contains risk and uncertainty. The prohibited gharar includes selling something non-existent or unknown. However, minor gharar may be overlooked if there is a need for it, such as selling a pregnant sheep or a padded robe. Some scholars hold that restaurants setting a fixed price for "all-you-can-eat" falls under minor gharar, which is permissible. But if a person eats more than usual, they must inform the restaurant owner, as this would then be considered significant gharar.