Patently, Dua, Prayer, Supplication, invocation is in essence an act of worship.
God says in the Quran: And your Lord says: "Call/supplicate/invoke upon/to Me (Arabic: odAAoonee); I shall answer your (prayer/invocation): Verily, those who
are too proud to worship (Arabic: AAibadatee) Me they will surely find themselves in Hell, in shame and in humiliation." [40:60]
Whenever, the error of directing one’s prayer (or any other acts of worship) to other than God/Allah is elucidated to and comprehended by the practitioner [of such prayers/acts] it falls into the scope of kufr
or Kafir i.e. wilfully rejecting guidance from God.
God says in the Quran: Whoever prays to another god alongside Him- a god for whose
existence he has no evidence- will face his reckoning with his Lord. Those who reject the truth (Arabic: alkafiroona) will not prosper. [223:117]
It is in this regard God warns: God does not forgive the worship of others beside Him - though He does forgive whoever He will for lesser sins- for whoever does this has gone far, far astray.
So the object of such devotion becomes a god or deity that is worshipped despite the erroneous claims to the contrary.
God says: They serve, besides God, things that hurt them not nor profit them, and they say: "These are our intercessors with God." Say: "Do ye indeed inform God of
something He knows not, in the heavens or on earth? Glory to Him! and far is He above the partners they ascribe (to Him)!” [10:18]
God further says in the Quran: Say: "Call on those - besides Him - whom you fancy: they have neither the power to remove your troubles from you nor to change them." Those whom they call upon do desire (for themselves) means of access to
their Lord which of those who are nearest and they hope for His Mercy and fear His Wrath: for the Wrath of thy Lord is something to take heed of. [17:56-57]
Allah knows best.
For Younger Readers
teaches in the Quran, the holy book of Muslims that: