What specific act of Sai Baba is mentioned in Chapter 40 as being the foundational inspiration for writing the Shri Sai Satcharitra?

Chapter 40 reveals that a specific, seemingly simple act by Sai Baba served as a profound inspiration for this book. The text describes how Sai, a saint, would set up a grinding stone in Shirdi, spread his legs, and grind grain. This image filled the author's mind with wonder and sparked a strong desire to describe all such deeds. This act is identified in the chapter as "the root of this book," with the author believing that by recounting these divine plays, the impurities and sins of the readers would be destroyed, which pleases God.