Is the marriage valid if the bride uttered the phrase "I give myself to you for mut'ah" in the presence of the Shiite marriage officiant, even though both spouses are Sunni and this phrase was not mentioned in the marriage contract?

The marriage contract takes place between two parties: the guardian (wali) and the husband or their representatives. Its formula is for the woman's guardian to say: "I give you in marriage [name of woman]," and for the husband to say: "I accept her marriage." If the contract is concluded with this formula, it is a valid marriage. The role of the ma'dhoun (marriage officiant) is to document the contract. People are accustomed to the ma'dhoun instructing the two parties on the formula of the contract, so he acts as an intermediary. What is mentioned after the conclusion of the contract, such as her saying, "I give myself to you in marriage," and similar phrases, does not harm the contract if it occurs after the contract has been concluded. Therefore, the marriage mentioned in the question is valid if it was concluded with its aforementioned lawful formula.