Musnad Ahmad 1153:347

Yunus narrated to us, he said: Layth narrated to us, from Yazid, from Musa ibn Sarjas, from al-Qasim ibn Muhammad, from Aisha, who said: I saw the Messenger of Allah, may Allah bless him and grant him peace, while he was dying, and beside him was a cup containing water. He would insert his hand into the cup, then wipe his face with the water, then say: "O Allah, assist me against the agonies of death."