Ar-Ra'd 13:14

Lahu daAAwatu alhaqqi wallatheenayadAAoona min doonihi la yastajeeboona lahum bishay-in illakabasiti kaffayhi ila alma-iliyablugha fahu wama huwa bibalighihi wamaduAAao alkafireena illa fee dalal

To Him [alone] is the supplication of truth. And those they call upon besides Him do not respond to them with a thing, except as one who stretches his hands toward water [from afar, calling it] to reach his mouth, but it will not reach it [thus]. And the supplication of the disbelievers is not but in error [i.e., futility].

True prayers are to be directed to Him alone; and those to whom they pray instead of Him do not respond to them at all, but they are like one who stretches his hands towards water so that it may reach his mouth (by itself), while it is not to reach it. And the prayer of the disbelievers (that they make to false gods) is nothing but straying in void.