"The Messenger of Allah said: 'When you see a funeral, stand up, and whoever follows it, let him not sit down until (the body) is placed (in the grave)." (Using translation from Nasāʾī 1917)
أَنَّ رَسُولَ اللهِ ﷺ قَالَ إِذَا رَأَيْتُمُ الْجَنَازَةَ فَقُومُوا فَمَنْ تَبِعَهَا فَلَا يَقْعُدْ حَتَّى تُوضَعَ