The Prophet ﷺ offered the Maghrib and ʿIsha' prayers together at Jam' (i.e. Al-Muzdalifa) with a separate Iqama for each of them and did not offer any optional prayer in between them or after each of them.  

جَمَعَ النَّبِيُّ ﷺ بَيْنَ الْمَغْرِبِ وَالْعِشَاءِ بِجَمْعٍ كُلُّ وَاحِدَةٍ مِنْهُمَا بِإِقَامَةٍ وَلَمْ يُسَبِّحْ بَيْنَهُمَا وَلاَ عَلَى إِثْرِ كُلِّ وَاحِدَةٍ مِنْهُمَا  

Messenger of Allah ﷺ offered the Maghrib and ʿIsha' prayers together at Al-Muzdalifa.  

أَنَّ رَسُولَ اللَّهِ ﷺ جَمَعَ فِي حَجَّةِ الْوَدَاعِ الْمَغْرِبَ وَالْعِشَاءَ بِالْمُزْدَلِفَةِ