Ibn Khuzaymah

In opposition to the statement of those who claim that one who catches an odd (rak‘ah) of the imam’s prayer must perform the two prostrations of forgetfulness: these two prostrations, if the praying person were to perform them, would be prostrations for intentional action, not for forgetfulness; because the one who catches an odd (rak‘ah) of the imam’s prayer intentionally sits in the first and third (rak‘ahs), as he is commanded to follow his imam, sitting in the place where he is commanded to sit. So how can one be forgetful who does what he is required to do and intentionally performs the action? And when it is invalid for him to be considered forgetful, it is impossible for the two prostrations of forgetfulness to be required of him, according to the report of the Prophet, peace and blessings be upon him: “When you come to the prayer, you must approach with calmness and dignity. Whatever you catch, pray, and whatever you miss, complete or make up.”

Hazrat Amr bin Wahb narrates that we were present in the service of Sayyiduna Mughirah bin Shu’bah (may Allah be pleased with him), so he was asked, "Has anyone from this Ummah, besides Sayyiduna Abu Bakr (may Allah be pleased with him), ever led the Prophet Muhammad (peace and blessings be upon him) in prayer?" He replied, "Yes, we were with the Prophet (peace be upon him) on a journey," then he narrated the complete hadith. Both of the Imam’s teachers narrate that then we mounted (and returned), and we saw that Sayyiduna Abdur Rahman bin Awf (may Allah be pleased with him) was leading the people in prayer. He had completed one rak’ah and was leading the second rak’ah. I wanted to inform him (of the arrival of the Prophet), but the Prophet (peace be upon him) forbade me. So, the rak’ah that we caught (with him), we performed, and the one that we missed, we completed. In the narration of Mu’ammal, it is stated that the rak’ah that was left, we completed it.