Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
Answering your question, The Permanent Committee for Scholarly Research and Ifta’ in Saudi Arabia, issued the following fatwa:
It is permissible for whoever misses congregational Prayer and cannot find anybody else to start a new congregation with, to pray (as a ma’mum) behind a person who is making up for the rak`ahs (units of Prayer) that they missed after the taslim (salutation of peace ending the Prayer) of the Imam.
The proof for the foregoing is that the Prophet (peace be upon him) was offering Prayer during the night and Ibn `Abbas came and prayed behind him. Moreover, offering Prayer in congregation is more rewarded.
Almighty Allah knows best.