Sunan an-Nasai Book 21, Hadith 1915

أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، عَنْ عَامِرِ بْنِ رَبِيعَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏ "‏ إِذَا رَأَى أَحَدُكُمُ الْجَنَازَةَ فَلَمْ يَكُنْ مَاشِيًا مَعَهَا فَلْيَقُمْ حَتَّى تُخَلِّفَهُ أَوْ تُوضَعَ مِنْ قَبْلِ أَنْ تُخَلِّفَهُ ‏"‏ ‏.‏

It was narrated from 'Amir bin Rabi'ah that the Prophet said:"When any one of you sees a funeral and is not walking with it, let him stand up until it has passed him, or until (the body) is placed (in the grave) before if passes him