Shaddad ibn Aws narrated: One day I saw the Prophet of Islam (PBUH) who was crying, and asked him:

Why are you crying? The Prophet (PBUH) replied: I fear from Shirk by my Ummah (Islamic nation) and that is why I am crying for. Beware that, (in here) Shirk (idolatry, polytheism) does not mean worshipping idols or to become the sun-worshipper, no; they will not worship the idols or the sun or the moon, or the stone, but they carry out their deeds with Riya (showing off, pretending) [1].

[1] Al-Mahajatal Baidha, Vol. 6, Page 141; Warram Collection, Vol. 2, page 233; Sharh Nahjul Balalghah, Ibn Abil Hadeed, Vol. 2, Page 179.

Source: en.shafaqna.com