Narrated 'Abdullah bin Mughaffal al-Muzani (RA):

The Prophet (ﷺ) said: "Pray before Maghrib, pray before Maghrib" then he said at the third time, "Whoever wishes (to)". He said so, because he did not like the people to take it as a Sunnah. [Reported by al-Bukhari].

وَعَنْ عَبْدِ اَللَّهِ بْنِ مُغَفَّلٍ الْمُزَنِيِّ ‏- رضى الله عنه ‏- عَنْ اَلنَّبِيِّ ‏- صلى الله عليه وسلم ‏-قَالَ : { صَلُّوا قَبْلَ اَلْمَغْرِبِ , صَلُّوا قَبْلَ اَلْمَغْرِبِ " ثُمَّ قَالَ فِي اَلثَّالِثَةِ : " لِمَنْ شَاءَ " كَرَاهِيَةَ أَنْ يَتَّخِذَهَا اَلنَّاسُ سُنَّةً } رَوَاهُ اَلْبُخَارِيُّ .‏ [1]‏