It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both); he said: "The Messenger of Allah (peace and blessings be upon him) had himself cupped and gave the cupper his wage; had it been unlawful, he (peace and blessings be upon him) would not have given it to him."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12791