Sayyiduna Ibn Abbas (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) had himself cupped while fasting and in the state of ihram, and he (peace and blessings be upon him) fainted. On that day he (peace and blessings be upon him) forbade the people from being cupped while fasting, for fear of weakness.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11272