We used to pray Maghrib with the Messenger of Allah ﷺ as soon as the sun disappeared behind the veil of the horizon.
قال حدثنا مكي حدثنا يزيد بن أبي عبيد
كنا نصلي المغرب مع رسول الله ﷺ إذا توارت بالحجاب
Its isnad is sahih, mentioned previously at 16484.