Name That Tune!

OK, last post tonight before I go beddy-bye...

Could anyone name the late 60s-early 70s song where it's a folksy guy singing while the tune is played on the piano? OK, yes, I know that's not enough to guess it except that (drum roll pleeeeaaaassse) the chorus is something like a gospel choir singing, "Oh happy day... Oh happy day".

Come on hotshots, tell me what it is so we both know.