Describe the origin and practice of the 'Satya-Sai vow' as detailed in Chapter 13.

The 'Satya-Sai vow' was a tradition started by the Patil as an act of gratitude after Sai Baba cured his illness. Chapter 13 explains that the Patil, inspired by the common practice of performing a Satyanarayan vow for deliverance from crisis, created a similar vow dedicated to Sai. Every Thursday, the Patil would perform this vow, which involved reading specific texts with devotion. Instead of the traditional Satyanarayan story, he would read the three chapters about Sainath written by Das Ganu in the 'Bhaktalilamrut.' He considered these chapters to be the 'Satya-Sai story,' the best among all vows. The text notes there is no difference between Narayan and Sai, and this practice, complete with offerings and celebration, became a regular custom in his village.