Whoever adores Allah through the fears of the fires of hell or in order to gain Paradise, whoever invokes Him in order that his share in the goods of the world be enlarged, or so that people should turn their faces toward him in order that he be glorified, or to avoid the evil which an oppressor afflicts upon him; or further, if he has heard a hadith of the Prophet according to which he who accomplishes a certain pious work, or recites a certain invocation, will receive from God some recompense -- whoever does this, his adoration is tainted, and it will not be acceptable to God except by virtue of His grace and of His generosity… God said, "Whoever hopes to encounter his Lord, let him do pious works and, in the adoration of his Lord, not associate any being with Him." (Koran 18:110) The things which I have mentioned are the "beings" which are associated with God. Now, God is, of all those that are associated in adoration, the One who absolutely transcends all association. That is why He prescribed to all His servants that they adore Him with a perfectly pure faith which implies the desire for no other recompense than His face…

(Abd el-Kader)