Source: Fatāwā Muḥammadīyah, Vol. 1, p. 367
Question:
If an imām, while leading prayer, forgets to perform rukūʿ in one rakʿah and completes the prayer with salām, but later the followers remind him of the mistake — what should be done? Should he repeat the entire prayer or only part of it?
Answer:
Al-ḥamdu lillāh, waṣ-ṣalātu wa-s-salāmu ʿalā Rasūlillāh, ammā baʿd:
In this case, the imām should:
❀ Repeat one rakʿah to make up for the one in which rukūʿ was missed.
❀ After completing it, he should recite tashahhud.
❀ Then, before salām, he should perform two sujūd al-sahw (prostrations of forgetfulness).
❀ Finally, he should complete the prayer with salām.
This way, the prayer will be complete and there is no need to repeat the entire prayer.
Evidence
This ruling is based on the famous ḥadīth of Dhū al-Yadayn:
The Messenger of Allah ﷺ once completed a prayer with fewer rakʿāt, then after being reminded, he performed the remaining rakʿāt and did not repeat the entire prayer.
(Ṣaḥīḥ al-Bukhārī; Jāmiʿ al-Tirmidhī; Tuḥfat al-Aḥwadhī, 1/307)
هٰذا ما عندي، والله أعلم بالصواب
