Hadith 1688
Ibn 'Umar (May Allah be pleased with them) said:
عن ابن عمر رضي الله عنهما قال سمعت رسول الله صلى الله عليه وسلم يقول: "من اقتنى كلبًا إلا كلب صيد أو ماشية فإنه ينقص فإنه ينقص من أجره كل يوم قيراطان" ((متفق عليه)). وفي رواية: قيراط.
The Messenger of Allah (ﷺ) said, "He who keeps a dog other than one for guarding the fields or herds or hunting, will lose two Qirat every day out of his rewards." [Al-Bukhari and Muslim].
In plain words
Keeping a dog without need, that is, not for guarding crops or livestock or for hunting, costs the owner a measure of reward each day. Keep only what serves a genuine purpose.
Reference : Riyad as-Salihin 1688 In-book reference : Book 17, Hadith 178