Musnad Ahmad 30:2867

Ishaq narrated to us, he said: Malik narrated to us, from Abu al-Zinad, from al-A'raj, from Abu Hurairah, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Among the worst of people is the two-faced person, who comes to these with one face, and to those with one face."