Musnad Abu Ya'la al-Mawsili 110:274

Zuhayr narrated to us, 'Abd al-Jabbar al-Khattabi narrated to us, 'Ubayd Allah ibn 'Amr narrated to us, from 'Abd al-Karim, from Qays ibn Hubtar, from Ibn 'Abbas, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "The price of a dog is foul." And he said: "If he comes to you seeking the price of a dog, fill his palm with dust."