Assalaamu alaykom. When we arrived at the mosque to pray the congregational prayer, the imam had already made the final salutation, but we saw some latecomers who caught some units of the prayer, my question is: What is better: form a second congregational prayer, or take one of the latecomers as our imam.

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 is His slave and Messenger.

It is better and more appropriate for you to form a second congregation and not pray behind a latecomer as a way of avoiding the difference of opinion among the scholars. Indeed, the scholars differed in opinion about the validity of the prayer behind a latecomer.

Shaykh Ibn ‘Uthaymeen after mentioning the difference of opinion in the Hanbali School in Sharh Al-Mustaqni’, said:

"We do not say that this matter is permissible, and we do not recommend it to people… but if they do so, then we do not say to them: your prayers are invalid; this is the most correct view; meaning that it is permissible, but this should not be done because it was not known to be done by our Salaf (righteous predecessors), so it is better to avoid it because we know that they [the Salaf] were more devoted than us in doing good, and were there any good in this matter, they would have preceded us to it."

Based on the above, the prayer behind a latecomer is valid, but it is better and more appropriate to avoid it as our Salaf were not reported to have done it, as Shaykh Ibn ‘Uthaymeen said.

Allah knows best.