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 aforesaid tradition has also been transmitted to the same effect by by Al Zuhri with a different chain of narrators beginning with Ibn Hanbal on the authority of Hammad. This version adds “With an iqamah for every prayer, he did not call adhan for the first prayer and he did not offer supererogatory prayer after any of them. The narrator Makhlad said “He did not call adhan for any of them.”  

بِإِقَامَةٍ وَاحِدَةٍ لِكُلِّ صَلاَةٍ وَلَمْ يُنَادِ فِي الأُولَى وَلَمْ يُسَبِّحْ عَلَى أَثَرِ وَاحِدَةٍ مِنْهُمَا قَالَ مَخْلَدٌ لَمْ يُنَادِ فِي 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