Sayyiduna Abu al-Darda' (may Allah be pleased with him) said that he (peace and blessings be upon him) vomited and then broke his fast. He (the narrator) said: I met Sayyiduna Thawban (may Allah be pleased with him), the freed slave of the Messenger of Allah (peace and blessings be upon him), in the mosque of Damascus, and I said to him: Sayyiduna Abu al-Darda' (may Allah be pleased with him) told me that the Messenger of Allah (peace and blessings be upon him) vomited and broke his fast. He said: He has spoken the truth, and I was the one pouring water for him.
This hadith is disputed with regard to its chain; if it is authentic, then it is to be understood as referring to a case where he vomited deliberately, and that his fast was a voluntary one.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8030