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  

the Messenger of Allah joined Maghrib and Isha; in Jam (Al-Muzdalifah), with one Iqamah, and he did not offer any voluntary prayers in between or after either of them.  

أَنَّ رَسُولَ اللَّهِ ﷺ جَمَعَ بَيْنَ الْمَغْرِبِ وَالْعِشَاءِ بِجَمْعٍ بِإِقَامَةٍ وَاحِدَةٍ لَمْ يُسَبِّحْ بَيْنَهُمَا وَلاَ عَلَى إِثْرِ كُلِّ وَاحِدَةٍ مِنْهُمَا  

the Messenger of Allah joined Maghrib and Isha; in Jam (Al-Muzdalifah), with one Iqamah, and he did not offer any voluntary prayers in between or after either of them. (Using translation from Nasāʾī 3028)  

أَنَّ رَسُولَ اللهِ ﷺ جَمَعَ بَيْنَ الْمَغْرِبِ وَالْعِشَاءِ بِجَمْعٍ بِإِقَامَةٍ وَلَمْ يُسَبِّحْ بَيْنَهُمَا وَلَا عَلَى أَثَرِ وَاحِدَةٍ مِنْهُمَا