Rafi' bin Khadij (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The earnings of the one who practices cupping are impure (lowly) 1, the wages of a prostitute are impure 2, and the price of a dog is impure 3." Imam Tirmidhi says:
1- The hadith of Rafi' (may Allah be pleased with him) is Hasan Sahih,
2- In this chapter, hadiths have also been narrated from 'Umar, 'Ali, Ibn Mas'ud, Abu Mas'ud, Jabir, Abu Hurairah, Ibn 'Abbas, Ibn 'Umar, and 'Abdullah bin Ja'far (may Allah be pleased with them),
3- Most of the people of knowledge act upon this. They have considered the price of a dog to be unlawful, and this is also the view of Shafi'i, Ahmad, and Ishaq bin Rahwayh. And some people of knowledge have permitted the price of a hunting dog.