Whoever mixes his deeds with any measure of shirk—such as calling upon someone other than Allah, seeking rescue from someone other than Allah, or slaughtering animals for someone other than Allah—has not been sincere in his worship. He is, in fact, a polytheist and is not upon the creed of Abraham (peace be upon him).
Many people who affiliate themselves with Islam today fall into major shirk: they supplicate to beings other than Allah, venerate graves and shrines, sacrifice and make vows to them, circumambulate them, seek their blessing, and cry out to the dead for help, among other practices, all the while claiming to be Muslims. Such individuals have not grasped the creed of Abraham (peace be upon him) on which their Prophet Muhammad (peace and blessings be upon him) stood. Either they never learned it, or they learned it and knowingly opposed it—Allah’s refuge is sought—and the latter is even more serious.
The creed of Abraham admits of no shirk whatsoever. Whoever adulterates his deeds with shirk is not upon the creed of Abraham, even if he professes it and claims to be a Muslim. It is therefore obligatory to know the creed of Abraham, to act in accordance with it, and to cling to it by worshipping Allah alone with unwavering sincerity, allowing no trace of either minor or major shirk into one’s worship.
This is the creed of Abraham (peace be upon him): the pure, upright faith that turns away from shirk entirely and devotes itself wholly to tawhid—that you worship Allah, dedicating the religion exclusively to Him.