Sahih Muslim Book 10, Hadith Number 3819.

Salim reported on the authority of his father (Allah be pleased with him) that Allah’s Messenger (may peace be upon him) said: He who kept a dog other than one meant for hunting or for the protection of the herd would lose two qirat of his deeds every day. Salim said: Abu Huraira (Allah be pleased with him) used to say: Or the dog meant for watching the field, and he was the owner of the land.