Is stipulating an option (Khiyār) for cancellation in a Waqf contract permissible?

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Stipulating an option for cancellation (Khiyār) in a Waqf contract invalidates the contract. Ahmad stated this ruling, which is also the view of Al-Shafi'i. This is because a condition that nullifies the contract's required effect is invalid, similar to stipulating the right to sell at will. Furthermore, since a Waqf involves transferring ownership to God, stipulating an option therein is invalid, similar to manumission (Citim). It also differs from lease agreements, which are transactional contracts allowing for options.