In the name of Allaah, the Most Merciful, the Ever Merciful
As-Salaamu ‘Alaykum
Is it permissible to buy or sell a dog? Is the revenue gotten from that dog lawful or forbidden? What is the ruling on buying a dog for guarding or hunting purposes?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu 'alyhi wa sallam, is His slave and Messenger.

The basic rule is that it is not permissible to sell, buy, or keep a dog and that its revenue (i.e., the money received for selling it)  is unlawful. It was narrated on the authority of Ibn ‘Umar that the Prophet, sallallaahu ‘alayhi wa sallam, said: “Whoever keeps a dog, except a dog for herding, hunting or farming, one Qeeraat (a mountain) will be deducted from his reward (from Allaah) each day.” [Al-Bukhari and Muslim] Abu Hurayrah in his narration, added: “or a dog for tilling”. It was also narrated that the Prophet, sallallaahu ‘alayhi wa sallam, forbade the revenue from a dog saying that it is evil.

For this general prohibition, some scholars, who form the majority, maintain that a dog’s revenue is absolutely forbidden, whether the dog is for guarding, herding, or whatever else. Other scholars said that it is permissible to buy and sell a dog and that its price is lawful as long as the dog is allowed to be kept for hunting, and other such (lawful) activities. They provided as evidence a narration on the authority of the Prophet, sallallaahu ‘alayhi wa sallam, that he “forbade the price of dogs, except for hunting dogs.” Ibn Hajar said that the narrators of this Hadeeth are trustworthy.

This is the predominant opinion.

Allaah Knows best.