What is the 'Satya-Sai vow' described in Chapter 13, and how did it come to be?

According to Chapter 13, the 'Satya-Sai vow' was a tradition started by the grateful Patil after Sai Baba miraculously cured his disease. The Patil adapted the existing practice of the Satyanarayan vow. On Thursdays, after bathing, he would read three specific chapters about Sainath from the Bhaktalilamrut, a book written by Das Ganu. He would make an offering of Naivedya and celebrate, seeing no difference between the Narayan of the original vow and Sai Baba. This practice, born from his deep gratitude, became a custom in his village.