Qatadah (may Allah have mercy on him) narrates from Abu al-Mutawakkil (may Allah have mercy on him) that Abu Sa'id (may Allah be pleased with him) said: Cupping (being done) for the fasting person is disliked only out of fear of weakness.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8267