Musnad Ahmad 27:1983

'Abdullah ibn al-Harith narrated to us, Hanzalah narrated to me, that he heard Salim ibn 'Abdullah saying: I heard 'Abdullah ibn 'Umar saying: I heard the Messenger of Allah (peace and blessings of Allah be upon him) saying: "Whoever acquires a dog, except for a hunting dog or a livestock dog, two qirats of his reward decrease every day."