Al-Imām al-Bukhārī - upon whom be mercy - narrates: Muḥammad ibn Salām reported to me; he said: Yazīd ibn Hārūn reported to us, from Yaḥyā, from Mūsā ibn ‘Uqbah, from Kurayb, the freed slave of Ibn ‘Abbās (may Allāh Almighty be content with both of them),
from Usāmah ibn Zayd (may Allāh Almighty be content with him), that: When the Messenger of Allāh ﷺ set out after standing at ‘Arafāt, he descended into a mountain pass and relieved himself. Usāmah ibn Zayd - may Allāh Almighty be content with him - said: “I was pouring water over him while he was performing Wuḍū’. I said, ‘O Messenger of Allāh, will you pray?’ He ﷺ replied, ‘The place of prayer is ahead of you.’”
حَدَّثَنِي مُحَمَّدُ بْنُ سَلاَمٍ، قَالَ أَخْبَرَنَا يَزِيدُ بْنُ هَارُونَ، عَنْ يَحْيَى، عَنْ مُوسَى بْنِ عُقْبَةَ، عَنْ كُرَيْبٍ، مَوْلَى ابْنِ عَبَّاسٍ عَنْ أُسَامَةَ بْنِ زَيْدٍ
أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم لَمَّا أَفَاضَ مِنْ عَرَفَةَ عَدَلَ إِلَى الشِّعْبِ، فَقَضَى حَاجَتَهُ. قَالَ أُسَامَةُ بْنُ زَيْدٍ فَجَعَلْتُ أَصُبُّ عَلَيْهِ وَيَتَوَضَّأُ فَقُلْتُ يَا رَسُولَ اللَّهِ أَتُصَلِّي فَقَالَ " الْمُصَلَّى أَمَامَكَ ".
Reference: Sahih Al Bukhari 181