If a person says that he does not make supplication because he relies on the divine decree, he is also erring, because Allah has made du’aa and asking means of attaining His forgiveness, mercy, guidance, support and provision.
If good is decreed for a person he will attain by du’aa what he cannot attain without du’aa. What Allah has decreed and knows with regard to His slaves’ circumstances and destinies is only decreed on the basis of means and decrees will be fulfilled at the appointed times.
There is nothing that happens in this world or in the Hereafter except on the basis of cause and effect; Allah is the Creator of both cause and effect. Disregarding the principle of cause and effect is contrary to reason.