Sunan an-Nasa'i, Hadith 2000 ⓘ
It was narrated from 'Ali bin Abi Talib that: mention was made of standing at the funeral until the body is placed in the grave. 'Ali bin Abi Talib said: "The Messenger of Allah stood, then he sat down."
أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، قَالَ حَدَّثَنَا خَالِدٌ، قَالَ حَدَّثَنَا شُعْبَةُ، قَالَ أَخْبَرَنِي مُحَمَّدُ بْنُ الْمُنْكَدِرِ، عَنْ مَسْعُودِ بْنِ الْحَكَمِ، عَنْ عَلِيٍّ، قَالَ : رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم قَامَ فَقُمْنَا، وَرَأَيْنَاهُ قَعَدَ فَقَعَدْنَا .
also referenced under: Book 21, Hadith 184 (In-Book) & Volume 3, Book 21, Hadith 2002 (DarusSalam)