According to Chapter 40, what specific event sparked the author's desire to write the Shri Sai Satcharitra?

According to Chapter 40, the initial inspiration for writing the Shri Sai Satcharitra came from witnessing one of Sai Baba's seemingly simple yet profound actions. The author describes the image of Sai, a saint, setting up a grinding stone, spreading His legs, and grinding grain. This vision filled the author's mind with wonder and sparked a strong desire to describe all of Sai's deeds. The chapter explains that this desire arose from the belief that by describing such acts, the author's own impurities and sins would be destroyed. This specific event of Sai grinding grain is identified in Chapter 40 as the very root of the book, initiating the entire project of chronicling Sai's life and leelas.