Scorsese got interested in Nass El Ghiwane when he saw Ahmed El Maânouni's 1981 film about the group, called Transes. Scorsese used their song, "Ya Sah," in his film 1989 The Passion of Christ. And Transes was the first film he restored when he got his World Cinema Foundation up and running in 2007.
You can watch the entire film here, but unfortunately, without subtitles. If you want those, you could watch it on Hulu Plus. Or buy it.