Examples given in Quran

 لَهُ دَعْوَةُ الْحَقِّ وَالَّذِينَ يَدْعُونَ مِن دُونِهِ لاَ يَسْتَجِيبُونَ لَهُم بِشَيْءٍ إِلاَّ كَبَاسِطِ كَفَّيْهِ إِلَى الْمَاء لِيَبْلُغَ فَاهُ وَمَا هُوَ بِبَالِغِهِ وَمَا دُعَاء الْكَافِرِينَ إِلاَّ فِي ضَلاَلٍ 13:14

(Fathe Muhammad Jalandari)
سودمند پکارنا تو اسي کا ہے اور جن کو يہ لوگ اس کے سوا پکارتے ہيں وہ ان کي پکار کو کسي طرح قبول نہيں کرتے مگر اس شخص کي طرح جو اپنے دونوں ہاتھ پاني کي طرف پھيلا دے تاکہ (دور ہي سے) اس کے منہ تک آ پہنچے حالانکہ وہ (اس تک کبھي بھي) نہيں آسکتا اور (اسي طرح) کافروں کي پکار بيکار ہے 13:14

(Muhammad Assad)
 13:14 Unto Him [alone] is due all prayer aiming at the Ultimate Truth, since those [other beings or powers] whom men invoke instead of God cannot respond to them in any way - [so that he who invokes them is] but like one who stretches his open hands towards water, [hoping] that it will reach his mouth, the while it never reaches him. Hence, the prayer of those who deny the truth amounts to no more than losing oneself in grievous error.13:14

(Yousaf Ali)
 13:14 For Him (alone) is prayer in Truth: any others that they call upon besides Him hear them no more than if they were to stretch forth their hands for water to reach their mouths but it reaches them not: for the prayer of those without Faith is nothing but (futile) wandering (in the mind).13:14