It is narrated from the holy Prophet of Islam (PBUH) who said:

Shirk (polytheism) is more hidden than the foot sound of the ants on the smooth stone in the dark night; and the lowest level of Shirk is to like the oppression (cruelty) of the oppressor, and be an adversary of the justice of a just person [1]. In another Hadith (narration), the holy Prophet (PBUH) said: The most dangerous thing that I fear for you is the minor Shirk. The companions asked: what is the minor Shirk? The holy Prophet (PBUH) replied: Hypocrisy; on the Day of Judgment when people are resurrected before God with their deeds (actions), God will tell the hypocrites: Go to those who you behaved hypocritically for their sakes and see if they can reward you [2]?

[1] Al-Mizan, Vol. 3, Appendix to Ayah 13 of Surah Aal-e-Imran, Quated from Aldurrul-Manthur, Vol. 2, Page 71.

[2] Jami-u-Sa’adat, Vol.2, Page 290; Beharul Anwaar, Majlesi, Vol. 72, Page 303, Hadith 50.

Source: en.shafaqna.com