What is the ruling on one who prays the last rak'ah of Maghrib with the Imam?

If the questioner joins the Imam during the bowing (rukūʿ), he has caught one rakʿah, and two rakʿahs remain for him. If he joins the Imam after the third bowing (i.e., during prostration or the final tashahhud), he must complete what he caught with the Imam, and then make up three rakʿahs after the Imam's taslīm. The difference in the manner of making up (qaḍāʾ) from the manner of performance (adāʾ) does not matter. He will receive the reward of congregational prayer, although it will be less than the reward of one who caught it from the very beginning.