Surah Rahman Verse 13
فَبِأَيِّ آلَاءِ رَبِّكُمَا تُكَذِّبَانِ
which of the favors of your lord would you deny?
Denying infers the several attitudes that the people adopt in respect of Allah Almighty’s blessings and manifestations of His might and His praiseworthy attributes (commendable qualities).
(12 Blessings (the Holy Qur’an, creation of man, teaching speech, well measured calculation of time, creation of plants and all kinds of trees, creation of the heaven, predominance of rules, creation of the earth with its characteristics, creation of kinds of fruit, creation of date palm, creation of crops, creation of flowers and sweet scented plants) along with the details, delicacies, and secrets concealed in each of them will suffice to make man show his gratitude toward Almighty and cause him to search for obtaining knowledge as to the source of all these Blessings.)
For Instance, some people do not at all admit that the Creator of all things is Allah Almighty. They think that all this is a mere byproduct of the matter, or an accidental happening, which is un-related with any wisdom and skill and workmanship. This is open denial.
Some other people do admit that the Creator of these things is Allah, but regard others beside Him also as associates in Godhead: they render thanks to others for His blessings: they adore others although they eat His provisions. This is another form of denial. Obviously, it would be the height of ingratitude if a person while admitting that a certain person had done him a favor rendered thanks to another, who had not in fact done him that favor, for this act of his would be an express proof that he regarded the other person as his benefactor whom he was rendering the thanks.
There are still others who acknowledge Allah alone as the Creator of all things and the Bestower of all blessings, but do not admit that they should obey the commands of their Creator and Sustainer and follow His injunctions. This is another form of ingratitude and denial of the blessings, for the person who behaves so denies the right of the Bestower of the blessing although he acknowledges the blessing itself.
Some other people neither disavow the blessing nor deny the right of the Bestower of the blessing, but in practice there is no appreciable difference between their conduct and the conduct of a denier. This is not verbal denial but denial in practice.