Narrated 'Abd Allah al-Muzani:
The Messenger of Allah ﷺ said: Pray two rak'ahs before the Maghrib prayer. He then said (again): Pray two rak'ahs before the Maghrib prayer, it applies to those who wish to do so. That was because he feared that the people might treat it as sunnah.

حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ عُمَرَ، حَدَّثَنَا عَبْدُ الْوَارِثِ بْنُ سَعِيدٍ، عَنِ الْحُسَيْنِ الْمُعَلِّمِ، عَنْ عَبْدِ اللَّهِ بْنِ بُرَيْدَةَ، عَنْ عَبْدِ اللَّهِ الْمُزَنِيِّ، قَالَ قَالَ رَسُولُ اللَّهِ ﷺ " صَلُّوا قَبْلَ الْمَغْرِبِ رَكْعَتَيْنِ " . ثُمَّ قَالَ " صَلُّوا قَبْلَ الْمَغْرِبِ رَكْعَتَيْنِ لِمَنْ شَاءَ " . خَشْيَةَ أَنْ يَتَّخِذَهَا النَّاسُ سُنَّةً .