Musnad Ahmad 27:1882

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from al-Zuhri, from Salim, from Ibn 'Umar, and Ayyub, from Nafi', from Ibn 'Umar, that the Prophet (peace and blessings of Allah be upon him) said: "Whoever keeps a dog, except for a dog for livestock or hunting, two qirats of his reward decrease every day."