(55) باب اسْتِحْبَابِ رَكْعَتَيْنِ قَبْلَ صَلاَةِ الْمَغْرِبِ
Anas b. Malik reported:
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'ahs 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 then.
Reference: Sahih Muslim 837
In-book reference: Book 6, Hadith 367
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 1821