Musannaf Ibn Abi Shayba 33:81

Abdullah ibn Idris narrated to us, from Isma'il ibn Abi Khalid, from Qays, who said: I heard Mustawrid, the brother of Banu Fihr, saying: I heard the Messenger of Allah (may Allah bless him and grant him peace) saying: "By Allah, the life of this world in comparison to the Hereafter is only like one of you placing his finger into the sea, then raising it; so let him see with what it returns."