It is narrated from Sayyiduna al-Mustawrid (may Allah be pleased with him), who was a Companion from Banu Fihr, that the Messenger of Allah (peace and blessings be upon him) said: "By the One in whose Hand is my soul, this world, compared to the Hereafter, is only like a man putting his finger into the sea, and then it comes back to him."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17853