Sahih al-Bukhari 1183
Narrated `Abdullah Al-Muzni:
The Prophet (ﷺ) said, "Pray before the Maghrib (compulsory) prayer." He (said it thrice) and in the third 
time, he said, "Whoever wants to offer it can do so." He said so because he did not like the people to 
take it as a tradition.
حَدَّثَنَا أَبُو مَعْمَرٍ، حَدَّثَنَا عَبْدُ الْوَارِثِ، عَنِ الْحُسَيْنِ، عَنِ ابْنِ بُرَيْدَةَ، قَالَ حَدَّثَنِي عَبْدُ اللَّهِ الْمُزَنِيُّ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏
"‏ صَلُّوا قَبْلَ صَلاَةِ الْمَغْرِبِ ‏"‏‏.‏ ـ قَالَ فِي الثَّالِثَةِ ـ لِمَنْ شَاءَ كَرَاهِيَةَ أَنْ يَتَّخِذَهَا النَّاسُ سُنَّةً‏.‏