Sayyiduna Rabi'ah bin Ka'b (may Allah be pleased with him) said: I used to serve the Messenger of Allah (peace and blessings be upon him) during the day, and when night came I would go to the door of the Messenger of Allah (peace and blessings be upon him) and spend the night near him (peace and blessings be upon him). I would continually hear him (peace and blessings be upon him) saying: "Subhan Allah, Subhana Rabbi (Glory be to Allah, glory be to my Lord)" until I grew tired or sleep overcame my eyes and I fell asleep. One day he (peace and blessings be upon him) said: "O Rabi'ah, ask of me and I will give you." I said: Give me some time so that I may think it over. Then I remembered that this world is perishing and coming to an end, so I said: O Messenger of Allah, I ask you to supplicate to Allah that He keep me away from Hell and admit me into Paradise. The Messenger of Allah (peace and blessings be upon him) fell silent, then said: "Who taught you this?" I said: No one taught me, but I know that this world is coming to an end and perishing, and because of the station you hold with Allah, I wished that you would supplicate to Allah. He (peace and blessings be upon him) said: "I will certainly do so, but help me by prostrating much."
Hadith Referenceالمعجم الكبير للطبراني / باب الراء / 4561