Ubadah bin Nusay (may Allah have mercy on him) said: I went in to Shaddad bin Aws (may Allah be pleased with him) and he was weeping. I said: O Abu Abd al-Rahman, what makes you weep? He said: Because of a hadith that I heard from the Messenger of Allah (peace and blessings be upon him); he (peace and blessings be upon him) was mentioning it: "Among the things I fear most for my Ummah are: associating partners with Allah, and hidden desire. A man begins the morning fasting, then he sees something he desires and fulfils it. And shirk is that some people do not worship a stone or an idol, but they do a deed in which they show off."
Hadith Referenceالمعجم الكبير للطبراني / باب الشين / 7114