Is the husband obligated to teach a Surah other than the one specified by the wife, if she requests it?

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The husband is not obligated to teach a different Surah if the wife brings one other than what was agreed upon, even if she requests instruction in a specific Surah. This is because the agreed-upon obligation pertains to a specific object (the Surah), and it is not incumbent upon him to perform the act on a different object, analogous to renting someone to sew a garment and then presenting a different garment for sewing. Furthermore, students vary greatly in their capacity to learn, and the husband has a specific purpose in teaching her, so he cannot be compelled to teach another.