Abu Dawud Book 14, Hadith Number 3171.
Chapter : Not known.
Narated By Thawban : An animal was brought to the Apostle of Allah (PBUH) while he was going with a funeral. He refused to ride on it. When the funeral was away, the animal was brought to him and he rode on it. He was asked about it. He said: The angels were on their feet. I was not to ride while they were walking. When they went away, I rode.