Voilà, je l'ai retrouvé c'est à la Rutgers University Librairies dans une interview de Stanley Crouch à Sonny Greer faite en janvier 1979 dans le cadre des fameuses "Oral Interview History" qui sont passionnantes...
On peut entendre Greer raconter l'épisode ici :
https://rucore.libraries.rutgers.edu/rutgers-lib/52263/#playback/M4A-8 mais il faut avancer jusqu'à 13:32 (jusqu'à 15:44 +/-) pour l'entendre parler de Django "l'homme qui pouvait prendre une guitare et la faire parler"...
On peut aussi lire l'histoire online sur un pdf à partir de la page 125 :
https://rucore.libraries.rutgers.edu/rutgers-lib/52263/SWF/read/L'épisode se passe à l'occasion de la tournée avec Duke Ellington dans la ville de Pittsburg dans un bar chic de Wiley Avenue...
"Boy but that cat he was something else. What king of man was he? Did he speak much english? None. Little tiny. So I body-guarded him. I remember one time we played a concert in Pittsburg. So he, a French boy living here, so he say "Come on Sonny, we go have a drink" I say all right. So we go in this high class joint, we stand at the bar, cat won't pay him mind. So you know, French hot, so he knocked on the bar. "Service". And the guy says "I can serve you, Mister " but he won't serve me. "What it is that for?" Had to drag the guy out of the bar. He wanted to create a scene. I said "Man, it's nothing. Forget it". He said, oh, a lot of french. I don't know what the hell it was but I know it was hot. So the guy after he found who we were, he apologized. "Come in" so I say "We don't want to come in your bar, Mister, You don't do me a favour. I spend the money. I owe you nothing. Forget it. You drink it". Anyway he couldn't even give it to me. I'm hot now. So we go, go back on Wiley Avenue. Ball! Ball! Ball!