Abu Darda told him that the Messenger of Allah ﷺ vomited and so broke his fast.The narrator said, "I met Thawban, the freed slave of the Messenger of Allah ﷺ, in the mosque of Damascus and said to him, 'Abu Darda informed me that the Messenger of Allah ﷺ vomited and broke his fast.'"Thawban replied, "He spoke the truth. I myself poured the water for his ablution."
أن أبا الدرداء حدثه أن رسول الله ﷺ لقاء فأفطر. قال: فلقيت ثوبان مولي رسول الله ﷺ في مسجد دمشق، فقلت له: إن أبا الدرداء أخبرني أن رسول الله ﷺ قاء فأفطر. قال: صدق أنا صببت عليه وضوءه.
Reported by Abu Dawud (2381), Tirmidhi (87), Nasai in Kubra (3107), and Ahmad (27502). Ibn Khuzayma graded it sahih (1957), and Ibn Hibban transmitted it from him (1097), as did Hakim (1/426) and Bayhaqi (4/220), all of them through Husayn Muallim, from Yahya bin Abu Kathir, "Abdul-Rahman bin Amr Uzai narrated to me, from Yaish bin Walid bin Hisham, his father narrated it to him," he said, "Madan bin Abu Talha narrated to me," and he related it. Some of them did not mention Abu Yaish between Yaish bin Walid and Madan bin Abu Talha. The correct position is to include him, as found in the narration of Husayn Muallim, and for this reason more than one scholar preferred his narration over that of others.Tirmidhi said, "Husayn Muallim polished this hadith well." He also said, "The hadith of Husayn is the most sahih thing on this subject." And in Ilal al-Kabir (1/168) it is reported from Bukhari that he said, "Husayn Muallim polished this hadith well."Hakim said, "This is a hadith that is sahih according to the criterion of the two Shaykhs, though they did not include it due to a disagreement among the companions of Abdul-Samad concerning it. Some of them said, 'from Yaish bin Walid, from his father, from Madan.' This is a mistake on the part of whoever said it, for Harb bin Shaddad and Hisham Dastawai both narrated it from Yahya bin Abu Kathir in the correct manner."He then narrated the hadith of Harb bin Shaddad and Hisham Dastawai without mentioning Yaish's father in the chain. Ibn Khuzayma had preceded him in this, saying, "The correct view is what Abu Musa narrated, namely that Yaish bin Walid heard directly from Madan, with no father between them" end quote.As for the wording "he vomited, so he broke his fast," the basic rule is that the letter fa here indicates causation. However, it is known from other hadiths that vomiting does not invalidate wudu, just as it does not break the fast. So perhaps he broke his fast due to the weakness that came over him, because along with vomiting a person may not be able to continue fasting for fear of harm or illness.As for Bayhaqi, he first judged the hadith to have a disputed chain of transmission, then said, "If it is sahih, then it should be understood as referring to a case where he vomited deliberately," as though ﷺ he had already committed himself to his fast. He then said, "It has also been narrated by another route from Thawban," which is the hadith that follows after the hadith of Fadala bin Ubayd.