Musnad Ahmad 834:9

Waki’ narrated to us, from Abu Sufyan ibn al-‘Ala’, who said: I heard al-Hasan narrating that 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 every pure black one among them." He said: A man said to him: "O Abu Sa’id, from whom did you hear this?" He said: He replied: "Abdullah ibn Mughaffal narrated it to me—and he swore [to it]—from the Prophet (peace and blessings of Allah be upon him) such and such time ago. And he had narrated it to us in that gathering."