Abu Hurairah (May Allah be pleased with him) said

The Messenger of Allah (ﷺ) said, "He who keeps a dog, will lose out of his good deeds equal to one Qirat every day, except one who keeps it for guarding the fields or the herd."

[Al-Bukhari and Muslim].

In a narration of Muslim, the Messenger of Allah (ﷺ) is reported to have said: "He who keeps a dog for any reason other than to guard his property (lands) or his flock of sheep, his good deeds equal to two Qirat will be deducted every day."