Ubadah bin Nusay (may Allah have mercy on him) said: I went in to Sayyiduna Shaddad bin Aws (may Allah be pleased with him) and he was weeping. He said: Two hadiths that I heard from the Messenger of Allah (peace and blessings be upon him). I said: What are those two things? He said: I went in to the Messenger of Allah (peace and blessings be upon him) and saw something in his face (peace and blessings be upon him) that grieved me. I said: O Messenger of Allah, what is this I see in your face? He (peace and blessings be upon him) said: "There are two things I fear for my Ummah after me: shirk and hidden desire. Listen! They will not worship the sun, the moon, a stone or an idol, but they will show off in their deeds." I said: O Messenger of Allah, is that shirk? He (peace and blessings be upon him) said: "Yes." I said: What is hidden desire? He (peace and blessings be upon him) said: "The servant begins the morning fasting, then one of his desires presents itself to him, so he fulfils it and abandons his fast."
Hadith Referenceالمعجم الكبير للطبراني / باب الشين / 7113