Where do all prayers go? Does God answer all prayers, even those of Muslims, Hindus, etc. although they pray to false gods? I heard from someone that the Bible says all prayers and praise reach God only. Is there scriptural evidence for this?
There is only one God. The gods of other religions are merely the product of the imagination of men. "Know therefore today, and take it to your heart, that the LORD, He is God in heaven above and on the earth below; there is no other" (Deuteronomy 4:39). Nor does God stand-in for the imaginary gods of men. When the prophets of Baal cried out their god, there was no one to answer. "To whom would you liken Me and make Me equal and compare Me, that we would be alike? Those who lavish gold from the purse and weigh silver on the scale hire a goldsmith, and he makes it into a god; They bow down, indeed they worship it. They lift it upon the shoulder and carry it; they set it in its place and it stands there. It does not move from its place. Though one may cry to it, it cannot answer; it cannot deliver him from his distress. Remember this, and be assured; recall it to mind, you transgressors. Remember the former things long past, for I am God, and there is no other; I am God, and there is no one like Me" (Isaiah 46:5-9).
God does not answer the prayers of sinners and the worship of other gods is sin. "The LORD is far from the wicked, but He hears the prayer of the righteous" (Proverbs 15:29).