Riyad us Saliheen: Hadith 1124

When we were in Al-Madinah, the moment the Mu'adhdhin finished the Adhan of the Maghrib prayer, the people hastened to the pillars of the mosque and performed two Rak'ah prayer behind them. A stranger coming into the mosque would think that the obligatory prayer had already been performed because of the number of people performing them.

[Muslim].