Answered by Shaykh Faraz Rabbani
I have seen people arriving after a prayer has been finished joining a latecomer who himself is making up rakats that he missed. is this permissible?
Walaikum assalam,
In the Hanafi school, it is not valid for the latecomer to lead others in prayer, and thus the prayer of those who follow behind him is invalid. [Shurunbulali, Maraqi al-Falah; Ibn Abidin, Radd al-Muhtar]
And Allah alone gives success.
Wassalam,
Faraz Rabbani