مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 596
Prayer
Observing Prayer Early in the Period - Section 1
وَعَنْ رَافِعِ بْنِ خَدِيجٍ قَالَ: كُنَّا نُصَلِّي الْمَغْرِبَ مَعَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَيَنْصَرِف أَحَدنَا وَإنَّهُ ليبصر مواقع نبله "
Rafi‘ b. Khadij said, “We used to observe the sunset prayer with God’s Messenger, then one of us would go away when it was still possible to see the distance of a bowshot.” (Bukhari and Muslim)
Mishkat al-Masabih, 596مُتَّفق عَلَيْهِ (الألباني)