Musannaf Ibn Abi Shayba 33:93

Abu Mu'awiyah narrated to us, from Sulayman ibn Farrukh, from al-Dahhak ibn Muzahim, who said: A man came to the Prophet, may Allah bless him and grant him peace, and said: "O Messenger of Allah, who is the most ascetic of people regarding the world?" He said: "He who does not forget the graves and the decay, and who abandons the best of the world's adornments, and prefers what remains over what perishes, and does not count tomorrow as part of his days, and counts himself among the dead."