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

Chapter 40 identifies a specific, symbolic act of Sai Baba as the root inspiration for the book. The author recalls the image of Sai, a great saint, setting up a grinding stone, spreading His legs, and grinding grain. This powerful scene filled the author's mind with wonder and ignited a strong desire to describe all of Sai's deeds. The underlying belief, as stated in the chapter, was that by singing the praises of God's devotees and describing their qualities, one's own impurities and sins would be destroyed, an act that is said to please God immensely.