Maghrib and Isha both prayers are offered togethor at:

مغرب اور عشاء دونوں نمازیں ایک ساتھ ادا کی جاتی ہیں

Muzdalfa

Mina

Arafat

Madina

None of these

Maghrib-Isha prayers are offered together at Muzdalifa on 9th Zill Hajj
...
Muzdalifah was the place where Prophet Adam (AS) the Maghrib and Isha prayers together.
Muzdalifah is also called Al-Ibtah, meaning flat area.
...
between 49 and 70 pebbles are collected from the ground at Muzdalifah and thrown at the three pillars at Mina, which represent the devil.
Muzdalifah (Arabic: مزدلفة) which is also known as al-Mashʿar or al-Mashʿar al-Ḥarām (المشعر الحرام) is a region between 'Arafat and Mina