Sahih Muslim Book 10, Hadith Number 3830.
Chapter : Conversion of currency and selling of gold for silver on the spot.
It is narrated on the authority of Humaid that Anas b. Malik was asked about the earnings of the cupper. He said: Allah’s Messenger (may peace be upon him) got himself cupped. His cupper was Abu Taiba and he (the Holy Prophet) commanded to give him two sa’s of corn. He (the Holy Prophet) talked with the members of his family and they lightened the burden of Kharaj (tax) from him (i.e. they made remission in the charges of their own accord). He (Allah’s Apostle) said: The best (treatment) which you take is cupping, or it is the best of your treatments.