Musnad Ahmad 30:770

'Attab ibn Ziyad narrated to us, Abdullah ibn al-Mubarak narrated to us, Ma'mar informed us, from Hammam ibn Munabbih, from Abu Hurayrah, from the Prophet, may Allah bless him and grant him peace: That he, when he would inhale water into his nose (istanshaqa), he would insert the water into his nostrils.