It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) had himself cupped and gave him his wage; had he (peace and blessings be upon him) known it to be impure (earnings), he (peace and blessings be upon him) would not have given him the wage.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12793