Can you explain the specific event that made the man who was averse to idol worship break his promise and bow to Sai Baba?

The man who accompanied Kaka Mahajani to Shirdi was a staunch devotee of the formless and had resolved not to bow to any saint. Chapter 35 details the precise moment this resolve was broken. As he set foot on the mosque's step, Sai Baba looked at him and spoke, saying, "Why have you come, sir." The content of the words was simple, but the tone of voice was miraculous. The man was astonished because it was a perfect imitation of his deceased father's exact vocal style. Hearing a voice he thought was lost forever coming from Baba's mouth was such a powerful and personal experience that he 'melted inside' and spontaneously bowed his head at Baba's feet, completely forgetting his earlier vow.