Sahih Bukhari
Funerals (Al-Janaaiz)
Volume: 002 / Book Number: 023 / Hadith Number: 394
Narrated 'Amir bin Rabi'a:,
The Prophet said, "Whenever you see a funeral procession, stand up till the procession goes ahead of you." Al-Humaidi added, "Till the coffin leaves you behind or is put down."