If the permanent imam of a mosque is suffering from an ailment that is expected to pass, he may lead the prayer while seated; the congregation should sit behind him, although their prayer remains valid even if they choose to stand.

Should the imam omit a pillar or a prerequisite over which the jurists disagree, doing so in reliance on a scholar’s opinion, his own prayer is still sound. Anyone who prays behind him while believing such an omission invalidates the prayer must repeat his own. No censure applies in matters open to ijtihād.

A woman may not lead a man in prayer,¹ nor may a discerning child (mumayyiz) lead an adult in an obligatory prayer. The child’s imamate is valid in supererogatory prayers, and in obligatory prayers when the followers are likewise discerning minors.

The leadership of someone who is in a state of ritual impurity or who carries a physical defilement, while knowing of it, is invalid. If neither he nor the congregation realize this until the prayer has ended,² only the congregation’s prayer is valid.

The imamate³ of an illiterate person—one who cannot recite Sūrat al-Fātiḥah correctly—is valid only over someone like himself. A voluntary prayer may be performed behind an imam who is praying an obligatory prayer, but not the reverse.

It is likewise permissible to perform a make-up (qaḍāʾ) prayer behind someone performing the current prayer, and vice versa, provided the two prayers share the same designation.

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It is valid for the imam to stand in the midst of the congregation, though the Sunnah is for him to stand slightly ahead of them. A single male follower stands to the imam’s right, level with him; it is invalid for him to stand behind or to the imam’s left while the space on the right is vacant. A woman stands behind him.