Rav Moshe has a teshuva (Iggerot Moshe, Even HaEzer 1,96), which many think is about Shlomo Carlebach, in which he said that songs written by a mumar are like a machine invented by a mumar.
Rav Moshe has a teshuva (Iggerot Moshe, Even HaEzer 1,96), which many think is about Shlomo Carlebach, in which he said that songs written by a mumar are like a machine invented by a mumar.