Musnad Ahmad 30:1604

Musa ibn Dawud narrated to us, Fulayh ibn Sulayman narrated to us, from Hilal ibn Ali, from Abd al-Rahman ibn Abi Amrah, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "If one of you cleans himself with stones (istijmar), let him use an odd number." "And if a dog laps from the vessel of one of you, let him wash it seven times." "And let not the surplus of water be withheld, so that the pasture may be withheld thereby." "And it is of the right of the camels that they be milked at the water on the day they arrive to drink."