Mishkat al-Masabih 4 Prayer كتاب الصلاة 582

وَعَنْ عَبْدِ اللَّهِ بْنِ مُغَفَّلٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسلم: «صلوا قبل صَلَاة الْمغرب رَكْعَتَيْنِ صَلُّوا قَبْلَ صَلَاةِ الْمَغْرِبِ رَكْعَتَيْنِ» . قَالَ فِي الثَّالِثَةِ: «لِمَنْ شَاءَ» . كَرَاهِيَةَ أَنْ يَتَّخِذَهَا النَّاسُ سنة

‘Abdallah b. Mughaffal reported the Prophet as saying, “Pray before the sunset prayer,” adding when saying it a third time, “This applies to those who wish to do so.” That was because he did not wish the people to treat it as a sunna . (Bukhari and Muslim.)