Musnad Ahmad 27:805

Waki’ narrated to us, Sufyan and ‘Abd al-Rahman narrated to us, from Sufyan, from ‘Abdullah ibn Dinar, from Ibn ‘Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever acquires a dog, except for a hunting dog or a dog for livestock, two qirats of his deeds will be deducted every day." ‘Abd al-Rahman said: "Deducted."