Latecomer following another latecomer in prayer
Question

                Al salam alykom.. 
      if i pray (ma'mom) and the immam finished the salaht.. but I didn't so I stood to complete
      my salaht .. then a person came to pray with me as a ma'mom ? Is my immamah correct?wa jazak allah kyran.
Praise be to Allah.If a person joins you wanting to pray with you, and you make the
    intention of leading him in prayer, this is OK.
The author of the book Nihaayat al-Zayn fi Irshaad
    al-Mubtadieen (p. 127) said: If the imaam says salaam then one latecomer
    decides to follow another latecomer in prayer, this is OK.
And Allah knows best.