Sahih al-Bukhari, Volume 7, Book 67, Hadith 391 (USC-MSA) ⓘ
Narrated `Abdullah bin `Umar: Allah's Messenger said, "If someone keeps a dog neither for guarding livestock, nor for hunting, his good deeds will decrease (in reward) by two Qirats a day.'
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنِ اقْتَنَى كَلْبًا إِلاَّ كَلْبَ مَاشِيَةٍ أَوْ ضَارٍ، نَقَصَ مِنْ عَمَلِهِ كُلَّ يَوْمٍ قِيرَاطَانِ " .
also referenced under: Book 72, Hadith 8 (In-Book) & Hadith 5482 (DarusSalam)