I suppose it depends what you mean by prayer. I can't imagine any religious person who wouldn't as a matter of course pray for sick people without waiting for permission. After all, no one would wait for the permission of all the combatants before praying for peace.

And I can't envisage anyone being offended by £Bless You" when they snbeeze. Or a "Goodbye" when parting. Both of which are, after all, prayers.

Praying with someone is a very different matter.