and the opening takbīr; for if they differ from him in intention or in entering the prayer, they have not joined him in prayer.
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If the omission concerns a Sunnah act of prayer, such as the middle sitting, he must perform the prostrations of forgetfulness. If it concerns an act of additional merit, such as raising the hands at the opening takbīr [and turning to the right in the closing salutation, he is not required to perform the prostrations of forgetfulness for that]. Even if raising the hands is described as a Sunnah act, it is not among the emphasized Sunnah acts and is more appropriately classed among acts of additional merit.
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If the omission concerns words, these likewise must be either obligatory, Sunnah, or of additional merit. If they are obligatory, such as the opening takbīr and the closing salutation, the prostrations of forgetfulness do not suffice, and the prayer is invalid. If they are Sunnah, such as reciting the surahs in addition to al-Fātihah, the prostrations of forgetfulness before the closing salutation suffice. If they are of additional merit, such as the qunūt supplication and glorifying Allah while bowing and prostrating, no prostrations are required.
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Their disagreement concerning someone who forgets a single takbīr in his prayer does not fall outside this principle. Rather, it follows from their disagreement over whether each takbīr is a separate Sunnah act or whether all the takbīrs together, apart from the opening takbīr, constitute a single Sunnah act in the prayer. Those who regard each takbīr as a separate Sunnah act require the prostrations for omitting one or two takbīrs. For omitting more than that, they require the prayer to be repeated if he neglects the prostrations until a long time has elapsed. Those who do not regard each takbīr as a separate Sunnah act, but consider all the takbīrs together a single Sunnah act in the prayer, do not require the prostrations for omitting a single takbīr. This is one of Ibn al-Qāsim’s two positions in al-Mudawwanah. Nor do they require the prayer to be repeated for omitting more than one takbīr if he neglects the prostrations until a long time has elapsed. This is explicitly stated by Ibn al-Qāsim in Abū Zayd’s transmission from him.