Musnad Ahmad 27:1056

Muhammad narrated to us, Shu'bah narrated to us, from Qatadah, from Abu al-Hakam, I heard Ibn 'Umar narrating from the Prophet, may Allah bless him and grant him peace, who said: "Whoever keeps a dog, except for a dog for crops, or livestock, or hunting, then indeed, a qirat from his reward decreases every day."