Musnad Abu Ya'la al-Mawsili 42:66

Narrated to us 'Abd al-A'la, narrated to us 'Abd al-Rahman ibn Zayd ibn Aslam, from his father, from 'Ata' ibn Yasar, from Abu Sa'id, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "The fasting person does not break his fast due to a wet dream, vomiting, or cupping."