Abdullah was a mystical Ethiopian Rabbi who taught Neville for five years.
In Neville's lecture A Lesson in Scripture you can read about his first meeting with the little known mystic in the highlighted section of the PDF. If you don't want to open the PDF you can read the article below.
I came into the world completely forgetful of the being that I AM. I had to. When I first met my friend Abdullah back in 1931, I entered a room where he was speaking and when the speech was ended he came over, extended his hand and said: “Neville, you are six months late.” I had never seen the man before, so I said: “I am six months late? How do you know me?” and he replied: “The brothers told me that you were coming and you are six months late.”
I was late because the one who told me of Abdullah was a Catholic priest. I loved him dearly, but I thought he was almost a moron. His father, a rumrunner in the days of prohibition, left him two million dollars, which he proceeded to lose on Wall Street the first year. The only wonderful thing he did was to take the last $15,000 and give it to a Catholic organization to care for his mother the rest of her earthly days. So, having no respect for his judgment, when he told me about Abdullah I postponed going to hear him until one day I could find no excuse. When Ab called me by name I said: “I don’t know you” and he replied: “Oh yes you do, but you have forgotten. We were together in China thousands of years ago, but you promised to completely forget in order to play the part you must play now.”
Last Friday night a lady gave me a letter saying: “The previous Monday as you stood on the platform I could not see you as Neville, but as an ancient Chinese philosopher. I have seen my friends change from moment to moment, but you remained changed during your entire lecture. This bothered me, so I questioned the experience on the way home and then I remembered. Several years ago in a psychic experience, I was walking up a hill with other students to attend a class. Falling away from the group, I saw an ancient Chinese in a white garment at my side. Beckoning me to follow him, we approached a cave where I saw a huge granite stone with a peak at the top. Two hands containing a cocoon covered the top of the stone. Removing the cocoon, the ancient Chinese broke it on the peak of the granite, and water, mixed with colorful oil, came out as life took on the sense of heat rising. Then the ancient Chinese took my hand and led me back to the group, where they had not realized that I had been away. “Now I know whose face you wore last Monday night.”
Well, that’s what Abdullah told me in 1931, but to this day I have no knowledge of it, because I swore in the beginning to empty myself completely of all memory and take on the form of a slave, but to have faith in him who sent me. Now knowing that he and I are one, I have no other place to go but back to myself, the sender. Having played every part I have completely wiped out the memory, but I know that no one can arrive at the end of the road until he has played it all. I do know from my intuitive knowledge that, just as an actor must feel the part he is playing and imagine himself the character he is depicting, you will imagine yourself into every part, and when the play is over for you, the signs will come to show you the being that you really are.
~ Excerpted from A Lesson in Scripture
In his lecture titled Changing the Feeling of 'I' Neville says "If I were called upon to name a man that I would consider my teacher, I would name Abdullah. I studied with that gentleman for five years."
Neville also described Abdullah as "black as the ace of spades" and said
that he was very proud of being a negro and didn't want any
modification of what God had made him and he would never allow anyone
to refer to him as a colored man.
Abdullah taught Neville that there was no cause outside of the arrangement of his own mind.