I heard the Prophet ﷺ saying, "If someone keeps a dog neither for hunting, nor for guarding livestock, the reward (for his good deeds) will be reduced by two Qirats per day."
سَمِعْتُ النَّبِيَّ ﷺ يَقُولُ مَنِ اقْتَنَى كَلْبًا إِلاَّ كَلْبٌ ضَارٍ لِصَيْدٍ أَوْ كَلْبَ مَاشِيَةٍ فَإِنَّهُ يَنْقُصُ مِنْ أَجْرِهِ كُلَّ يَوْمٍ قِيرَاطَانِ