Musnad Ahmad 430:2

Isma'il narrated to us, he said: Yunus informed us, from al-Hasan, from Abdullah ibn Mughaffal, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Were it not that dogs are a nation among the nations, I would have ordered their killing. So kill from among them the solid black one. And whatever people take a dog that is not a dog for cultivation, hunting, or livestock, a qirat will be deducted from their rewards every day." He said: "And we used to be ordered to pray in the resting places of sheep, and we do not pray in the resting places of camels, for they were created from the devils."