Musnad Ahmad 834:32

'Abd al-A'la narrated to us, from Yunus, 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 commanded that they be killed. So kill the solid black one. And whatever people keep a dog that is not a dog for hunting, or for crops, or for livestock, a qirat will be deducted from their rewards every day." And the Messenger of Allah (peace and blessings of Allah be upon him) said: "Pray in the resting places of sheep, and do not pray in the kneeling places of camels, for they were created from the devils."