The sunan prayers and their virtues - Section 3 Mishkat al-Masabih 1180
Arabic hadith text
وَعَنْ أَنَسٍ قَالَ: كُنَّا بِالْمَدِينَةِ فَإِذَا أَذَّنَ الْمُؤَذِّنُ لِصَلَاةِ الْمَغْرِبِ ابْتَدَرُوا السَّوَارِيَ فَرَكَعُوا رَكْعَتَيْنِ حَتَّى إِنَّ الرَّجُلَ الْغَرِيبَ لَيَدْخُلُ الْمَسْجِدَ فَيَحْسَبُ أَنَّ الصَّلَاةَ قَدْ صُلِّيَتْ مِنْ كَثْرَةِ مَنْ يُصَلِّيهمَا. رَوَاهُ مُسلم
Translation
Anas said, “When we were in Medina, the moment the mu’adhdhin made the call to the sunset prayer the people hastened to the pillars of the mosque and prayed two rak'as, with the result that any stranger coming into the mosque would think that the obligatory prayer had been observed owing to the number who were praying them.” Muslim transmitted it.