Surely Syirik is great injustice.

Has told us Abu Al Walid said, has told us the Shu'bah and has also narrated this same hadith,

Has told me Bisyir bin Khalid Abu Muhammad Al 'Asykari said, has told us Muhammad bin Ja'far of the Syu'bah from Solomon from Ibrahim from Alqama from Abdullah said:

When the verse goes down: "Believers and do not mix up their faith with injustice" the Companions of the Messenger of Allaah (peace and blessings of Allaah be upon him) said:

"Who among us is not doing zhalim??

So Allah 'azza wajalla decreed (His word)::

"Surely Syirik is great injustice".
(Luqman: 13)
(Bukhari 31)