This thread is intriguing.
For me "soul" is all about the voice and the emotions that a singer conveys to the listener.
But maybe a couple of instrumentals that might be considered soulful , King Curtis: Soul Serenade,
Jimmy McGriff :Turn blue,
Art Blakey & the Jazz Messengers : Moanin'.
Even though I really like all the above, I still keep drifting back to Ernestine Andersons rendition of "Moanin".
I love this music!