Someone vomited a little while performing Wudhoo' (ablution), when the Athaan (call to prayer) of Fajr was being pronounced; would his fasting during that day be valid?
All perfect praise be to Allah, the Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, salallaahu alayhi wa sallam, is His Slave and Messenger.
The true dawn, which is the time when light spreads horizontally rightward and leftward, is the time when a fasting person has to stop eating, drinking, and anything else that would break his fast. Consequently, if the Athaan that is referred to was pronounced after the rise of the true dawn on the one hand, and the vomiting referred to was intentionally initiated after the person heard or was hearing the Athaan, on the other hand, then the fast of that day would be invalid and has to be made up for. However, if the vomiting was not intentionally initiated, the fast would be valid.
Allah Knows best.