Sunan an-Nasa'i, Hadith 1954 ⓘ
It was narrated from 'Upbah that: the Messenger of Allah went out one day and offered the funeral prayer for the people f Uhd, then he went to the Minbar and said: "I am your predecessor and I am a witness over your."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنْ يَزِيدَ، عَنْ أَبِي الْخَيْرِ، عَنْ عُقْبَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم خَرَجَ يَوْمًا فَصَلَّى عَلَى أَهْلِ أُحُدٍ صَلاَتَهُ عَلَى الْمَيِّتِ ثُمَّ انْصَرَفَ إِلَى الْمِنْبَرِ فَقَالَ " إِنِّي فَرَطٌ لَكُمْ وَأَنَا شَهِيدٌ عَلَيْكُمْ " .
also referenced under: Book 21, Hadith 138 (In-Book) & Volume 3, Book 21, Hadith 1956 (DarusSalam)