´It was narrated from 'Abdullah bin Mughaffal that the Prophet said:` "Whoever keeps a dog, except a dog for hunting, herding livestock or farming, one Qurat will be deducted from his reward each day."
Explanation & Benefits
Hafiz Muhammad Ameen
It is possible that the decrease in good deeds is either due to causing harm to people, or because the angels do not enter the house, since the arrival of angels creates an inclination towards good deeds among the household. Or it may be due to disobedience of a legal (shar‘i) command, or because the dog keeps putting its mouth in the household utensils and the owner does not realize it, etc. In short, Allah knows best the real reason; nothing definitive can be stated.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 4293