We should pray for those of another faith. Jesus tells us to do these things together: Preach the gospel, cast out devils, heal the sick, and cleanse the lepers.
don't encourage them to pray to Buddha or St. Whoever or burn the candles from aisle 5 at the grocery mart.
Tell them that the God of Abraham holds the keys to death and the grave and that JESUS gave authority to those who believe in Him.
We now live in a pagan, corrupted land. So did Daniel, Jeremiah, and many of the prophets (major topics for them). They did not encourage any idol worship. They warned that we need to serve the Lord, and they all, in addition to their watchman duties, foretold of the 1st and 2nd comings of Jesus.
The Word is very clear on other religions: we should not participate, and should not marry non-believers (their pagan ways corrupted even King Solomon). It is we who Jesus gave the power to bind and to loose... When you say something is okay... by passively allowing it without comment, or by encouraging it, then YOU release it using your own authority.
So, do not encourage prayer to other than: Jesus/Holy Spirit/Father in Heaven