Musnad Abu Ya'la al-Mawsili 42:186

Abu Khaythama narrated to us, Jarir ibn Abd al-Hamid narrated to us, from Suhayl ibn Abi Salih, from his father, from Abu Sa’id al-Khudri, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "If you follow a funeral procession, do not sit down until it is placed [on the ground]." Suhayl said: I saw Abu Salih not sitting down until it was placed down from the shoulders of the men.