The Prophet (ﷺ) said: The earnings of a cupper are impure, the price paid for a dog is impure, and the hire paid to a prostitute is impure.
Sunan Abi Dawud Book 24, Hadith 6
← Previous Hadith You have brought what is good from this man. Then they brought a lunatic in chains. He recited Surat al-Fatihah over him three days, morning and evening. When he finished, he collected his saliva and then spat it out, (he felt relief) as if he were set free from a bond. They gave him something (as wages). He then came to the Prophet (ﷺ) and mentioned it to him. The Messenger of Allah (ﷺ) said: Accept it, for by my life, some accept it for a worthless charm, but you have done so far a genuine one.

Sunan Abi Dawud Book 24, Hadith 5 Next Hadith → Muhayyisah asked permission of the Messenger of Allah (ﷺ) regarding hire of the cupper, but he forbade him. He kept on asking his permission, and at last he said to him: Feed your watering camel with it and feed your slave with it.

Sunan Abi Dawud Book 24, Hadith 7