Messenger of Allah ﷺ said, "Whoever keeps a dog, one Qirat of the reward of his good deeds is deducted daily, unless the dog is used for guarding a farm or cattle."  

قَالَ رَسُولُ اللَّهِ ﷺ «مَنْ أَمْسَكَ كَلْبًا فَإِنَّهُ يَنْقُصُ كُلَّ يَوْمٍ مِنْ عَمَلِهِ قِيرَاطٌ إِلاَّ كَلْبَ حَرْثٍ أَوْ مَاشِيَةٍ۔»  

Abu Sufyan bin Abu Zuhair, a man from Azd Shanu'a and one of the companions of the Prophet ﷺ said, "I heard Messenger of Allah ﷺ saying, 'If one keeps a dog which is meant for guarding neither a farm nor cattle, one Qirat of the reward of his good deeds is deducted daily." I said, "Did you hear this from Messenger of Allah ﷺ?" He said, "Yes, by the Lord of this Mosque."  

أَنَّهُ سَمِعَ سُفْيَانَ بْنَ أَبِي زُهَيْرٍ رَجُلاً مِنْ أَزْدِ شَنُوءَةَ وَكَانَ مِنْ أَصْحَابِ النَّبِيِّ ﷺ قَالَ سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ مَنِ اقْتَنَى كَلْبًا لاَ يُغْنِي عَنْهُ زَرْعًا وَلاَ ضَرْعًا نَقَصَ كُلَّ يَوْمٍ مِنْ عَمَلِهِ قِيرَاطٌ قُلْتُ أَنْتَ سَمِعْتَ هَذَا مِنْ رَسُولِ اللَّهِ ﷺ قَالَ إِي وَرَبِّ هَذَا الْمَسْجِدِ