Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 2090
It is narrated on the authority of 'Amir Ibn Rabi'a (may Allah be pleased with him) that the Prophet (may peace be upon him) said: Whenever you see a funeral procession, stand up for that until it moves away or is lowered on the ground.