Musnad Abu Ya'la al-Mawsili 159:13

Abu Khaythama narrated to us, Sufyan narrated to us, from Abu al-Zinad, from al-A'raj, from Abu Hurayrah, attributing it to the Prophet (may Allah bless him and grant him peace), who said: "If one of you looks at someone who has been favored over him in wealth and physique, then let him look at someone who is below him in wealth and physique."