Abu Ali al-Hafiz (may Allah have mercy on him) said: I said to Abdan al-Ahwazi: Is it authentic that the Prophet (peace and blessings be upon him) was cupped while fasting? He said: I heard Abbas al-Anbari (may Allah have mercy on him) say: I heard Ali bin al-Madini (may Allah have mercy on him) say: The hadith of Abu Rafi' from Abu Musa (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said, "The cupper and the cupped have both broken their fast", is authentic.
And it reached me from Abu Isa al-Tirmidhi that he said: I asked Abu Zur'ah about the hadith of Ata' from Abu Hurayrah in marfu' form, and he said: It is a hasan (good) hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8298