Sayyiduna Abu Rafi' (may Allah be pleased with him) narrates: I entered upon Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him) while he was being cupped at night in Ramadan. I said: Why was this (not done) during the day? He said: Do you order me to shed my blood while I am fasting, when I have heard the Messenger of Allah (peace and blessings be upon him) say: "The hajim and the mahjum (the one who cups and the one who is cupped) have broken their fast"?
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8287