Sahih al-Bukhari 1183
Sahih al-Bukhari · Book 19: Prayer at Night (Tahajjud) · The (optional) salat before the Maghrib prayers
Narrated `Abdullah Al-Muzni:
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.
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.