From Sahih Muslim (Hadith 2218):
It is narrated on the authority of 'Amir ibn Rabi'a (may Allah be pleased with him) that the Prophet (ﷺ) said:Should any one of you come across a funeral procession, and if he does not intend to accompany it, he must stand up until it passes by him or is placed upon the ground before it passes him
Reference: Muslim 2218