The Book Pertaining to Piety and Softening of Hearts (Kitab Al-Zuhd wa Al-Raqa'iq)
Muslim :: Book 42 : Hadith 7070
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: Look at those who stand at a lower level than you but don't look at those who stand at a higher level than you, for this would make the favours (conferred upon you by Allah) insignificant (in your eyes). Abu Mu'awiya said: Upon you.