Sayyiduna Mughira (may Allah be pleased with him) said: When we reached the people, they had already established the prayer and Sayyiduna Abdur Rahman bin Awf (may Allah be pleased with him) was leading them in the Fajr prayer and had gone into ruku‘. When he sensed the arrival of the Prophet Muhammad (peace and blessings be upon him), he began to move back, but the Messenger of Allah (peace and blessings be upon him) gestured with his blessed hand, so he completed the prayer. Then, when he finished with salam, the Messenger of Allah (peace and blessings be upon him) stood up and I also stood up, and we performed the rak‘ah that we had missed. Abu Muhammad Imam Darimi (may Allah have mercy on him) said: In terms of fatwa, I hold the opinion of the people of Kufa, that the rak‘ah which is missed should be made up, meaning it will be considered as qada, and the rak‘ah performed with the imam will be considered as the second.
Hadith Referenceسنن دارمي / من كتاب الصللاة / 1373
Hadith Takhrijاس حدیث کی سند صحیح ہے۔ دیکھئے: [مسلم 274/81] ، [ابن حبان 1326]
Brief Explanation
(Commentary on Ahadith 1371 to 1373)
This is the opinion of Imam Darimi rahimahullah and the scholars of Kufa, and the correct view is that the rak‘ah performed with the imam will be counted as the first rak‘ah, and the remaining ones will be the second or third in order.
From this hadith, it is understood that if the follower (muqtadi) is masbuq (i.e., has missed some rak‘ahs), he should complete his prayer after the imam has said the salam. Furthermore, this hadith demonstrates the forbearance, patience, and exemplary character of the Messenger of Allah sallallahu alayhi wa sallam.
He sallallahu alayhi wa sallam did not reproach anyone for leading the prayer. May my father and mother be sacrificed for him, sallallahu alayhi wa alihi wa sahbihi wa sallam, countless salutations. And this delay of the Prophet sallallahu alayhi wa sallam was due to the need to relieve himself.