Chapter 38: The Book of Distribution of Al-Fay'
It was narrated from 'Amr bin Shu' aib, from his father, from his grandfather, that: the Messenger of Allah went to a camel, and took a hair from its hump between his fingers and said: "I am not entitled to take anything from the Fay, not even this, except the Khumus, and the Khumus will come back to you."
Sunan an-Nasa'i 4139