The Youtube clip below haunts the mind. Recorded spontaneously on 23 Dec 1975 after the memorial service in London of Mongezi Feza, who had died of pneumonia while a patient in a mental hospital in Epsom, Surrey, aged just 30.
Wanna read more? There's loads on the Blue in the Air blog and the Matsuli blog. A Jazzwise review is at here of the CD version which came out last autumn.
Or just listen.