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It was narrated from Usmah bin Zaid that when the Prophet (ﷺ) departed from Arafat he turned toward the mountain pass. I said to him: "Are you going to pray Magrib?" He said: "The prayer place is still ahead of you."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ إِبْرَاهِيمَ بْنِ عُقْبَةَ، عَنْ كُرَيْبٍ، عَنْ أُسَامَةَ بْنِ زَيْدٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم حَيْثُ أَفَاضَ مِنْ عَرَفَةَ مَالَ إِلَى الشِّعْبِ قَالَ فَقُلْتُ لَهُ أَتُصَلِّي الْمَغْرِبَ قَالَ " الْمُصَلَّى أَمَامَكَ " .
sunnah.com