Waman athlamu mimmani iftara AAala Allahi kathiban aw kaththaba bi-ayatihi innahu la (surah Anam: 21)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(6:21) And who could be more wrong-doing than he who either foists a lie on Allah *15 or gives the lie to His signs?  *16Surely such wrong-doers shall not attain success.

Wa man azlamu mim manif tara `alal laahi kaziban aw kazzaba bi Aayaatih; innahoo laa yuflihuz zaalimoon

*15). This refers to those who asserted that there were also other beings which shared with God in His godhead, were possessed of divine attributes and powers, and rightly deserved to claim from man worship and absolute service. It is also a slander to claim that God has selected certain beings to be His chosen intimates and that lie has commanded - or is at least agreeable to the idea - that they should he considered to possess divine attributes, and that people should serve and revere them as they would serve and revere God, their Lord.
*16). By 'signs of God' are meant the signs found within man's own being, as well as those scattered throughout the universe. They also include the signs which are manifest from the lives and achievements of the Prophets, as well as those embodied in the Scriptures. All these point towards one and the same truth - that in the entire realm of existence there is one God alone and that all else are merely His subjects. Who could be more unjust than one who, in utter disregard of all these signs, invests others than the One True God with attributes of godhead, considering them to merit the same rights as God. And does so merely on grounds of either conjecture, or speculation or out of blind adherence to the beliefs of his forefathers although there is not so much as a shred of evidence founded on true knowledge, observation or experience in support of such beliefs. Such a person subjects truth and reality to grave injustice. He also wrongs his own self and everything else in this universe with which he has to deal on the basis of this false assumption.