Sahih Bukhari Volume 009, Book 089, Hadith Number 266.
Narrated By Tarif Abi Tamima : I saw Safwan and Jundab and Safwan's companions when Jundab was advising. They said, "Did you hear something from Allah's Apostle?" Jundab said, "I heard him saying, 'Whoever does a good deed in order to show off, Allah will expose his intentions on the Day of Resurrection (before the people), and whoever puts the people into difficulties, Allah will put him into difficulties on the Day of Resurrection.'" The people said (to Jundab), "Advise us." He said, "The first thing of the human body to purify is the abdomen, so he who can eat nothing but good food (Halal and earned lawfully) should do so, and he who does as much as he can that nothing intervene between him and Paradise by not shedding even a handful of blood, (i.e. murdering) should do so."