Assalaamu alaykum. While praying the Maghrib prayer, the imam's ablution broke, and another person took the lead with a new recitation of Al-Faatihah. When we finished, it was said that we should prostrate because the previous imam had commenced reciting Al-Faatihah and that the second imam, instead of continuing from where the first one had stopped, started anew. Kindly share the valid position according to the Shariah.

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger. 

The prayer is valid in any case. The imaam followed the scholarly view that the one being led in the prayer is obliged to recite the Faatihah himself (i.e. that it is not sufficient that the imaam recited it). This is the view adopted at Islamweb, contrary to the other view in this regard; that the one being led is not required to recite it (and that the imaam's recitation suffices). According to this second view, the new imaam should carry on from the part where the first imaam had stopped if he knows it; otherwise, he starts the recitation from the beginning.

The fatwa of the Permanent Committee for Islamic Research and Fataawa reads, “If the imaam died or broke his ablution during the prayer, it is allowed for one of those being led to succeed him and complete the prayer, and he should recite the Faatihah from the beginning. It is also allowed for him to carry on from where the first imaam had stopped if he (the second imaam) had already recited the Faatihah, according to the most likely correct view of the two opinions in this regard.”

In his commentary on Mukhtasar Khaleel, Al-Kharshi said:

“The second imaam should continue the prayer and start from the part where the first imaam had stopped in the audible prayers. If the first imaam had not recited anything, the second imaam should start the recitation from the beginning. If the prayer is inaudible, the second imaam should start the Faatihah from the beginning even if the first imaam had remained in the standing position for a period of time during which he could have recited it because it is possible that he had forgotten to recite it or recited it slowly and did not finish it. This is the meaning of his (Khaleel's) statement 'He should start the Faatihah if he did not know that he (the first imaam) had completed his recitation', but if he knew that like if the first imaam informed the second imaam of the part at which he stopped, or if the second one was standing near him and could hear his recitation during the (inaudible) prayer, then he should carry on from where the first imaam stopped, as is the case with the audible prayer. His (Khaleel's) statement 'He should recite means that it is recommended for him to recite Al-Faatihah anew in this situation. This is the view of some scholars who held that opinion after invetigation. The apparent meaning of his (Khaleel's) words is that the second imaam is allowed to recite Al-Faatihah again even if the first imaam did so; however, this is not acceptable; as it is impermissible to repeat the verbal pillar in the prayer (i.e. reciting Al-Faatihah); despite the fact that it does not invalidate the prayer.” [Sharh Mukhtasar Khaleel]

Allah knows best.