Ibn Majah 2165

[Sahih] The hadith has corroborating narrations in Nasai, 7/310, 311, Sales, Selling the Stud Fee of a Camel, no. 4677, and elsewhere. Muslim also narrated it, no. 1568, and elsewhere, from Rafi bin Khadij, who attributed it to the Prophet, "The earnings of a cupper are impure."