Hadith 455:4
'Attab ibn Ziyad narrated to us, he said: 'Abdullah narrated to us, Al-Sari ibn Yahya narrated to us, from Kathir ibn Ziyad, he said: Ibn 'Abasah said: I saw the Messenger of Allah (may Allah bless him and grant him peace) rinse his mouth and sniff water into his nose while fasting.
حدثنا عتاب بن زياد، قال: حدثنا عبد الله، حدثنا السري بن يحيى، عن كثير بن زياد، قال: قال ابن عبسة: رأيت رسول الله صلى الله عليه وسلم " مضمض واستنشق في رمضان "