Hadith 4:619
Ghundar narrated to us, from Shu'bah, from Hammad, regarding the fasting person who rinses his mouth and water enters his throat: If his ablution was obligatory, then there is nothing upon him. But if he rinsed his mouth for other than that (i.e., not for obligatory ablution), then he must repeat (the fast).
حدثنا غندر عن شعبة عن حماد في الصائم تمضمض فدخل الماء حلقه إن كان وضوء ( ( ( وضوؤه ) ) ) واجب ( ( ( واجبا ) ) ) فليس عليه شيء وإن كان مضمض عن غيره فإنه يعيد