Musnad Ahmad 595:5

Ja'far ibn 'Awn narrated to us, he said: Isma'il narrated to us, from Qays, he said: I heard al-Mustawrid, the brother of Banu Fihr, saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "By Allah, the worldly life in comparison to the Hereafter is only like one of you dipping his finger into the sea; so let him see with what it returns."