Sayyiduna Thawban (may Allah be pleased with him), the freed slave of the Messenger of Allah (peace and blessings be upon him), narrates that the Messenger of Allah (peace and blessings be upon him) passed through al-Baqi', and he (peace and blessings be upon him) passed by a man who was being cupped. It was the eighteenth or the sixteenth of Ramadan, and he (peace and blessings be upon him) said: "The cupper and the cupped have broken their fast."
(Ibn Jurayj narrates from Makhul that an elder of the tribe told him that Sayyiduna Thawban (may Allah be pleased with him), the freed slave of the Messenger of Allah (peace and blessings be upon him), informed him that the Prophet (peace and blessings be upon him) said: "The cupper and the cupped have broken their fast.")
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8285