صَحِيحُ مُسْلِمٍ
Sahih Muslim 837
The Book of Prayer - Travellers
It is recommended to pray two rak`ah before Maghrib
وَحَدَّثَنَا شَيْبَانُ بْنُ فَرُّوخَ، حَدَّثَنَا عَبْدُ الْوَارِثِ، عَنْ عَبْدِ الْعَزِيزِ، - وَهُوَ ابْنُ صُهَيْبٍ - عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ كُنَّا بِالْمَدِينَةِ فَإِذَا أَذَّنَ الْمُؤَذِّنُ لِصَلاَةِ الْمَغْرِبِ ابْتَدَرُوا السَّوَارِيَ فَيَرْكَعُونَ رَكْعَتَيْنِ رَكْعَتَيْنِ حَتَّى إِنَّ الرَّجُلَ الْغَرِيبَ لَيَدْخُلُ الْمَسْجِدَ فَيَحْسِبُ أَنَّ الصَّلاَةَ قَدْ صُلِّيَتْ مِنْ كَثْرَةِ مَنْ يُصَلِّيهِمَا .
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.
Sahih Muslim, 837Sahihصحيح