Explain the origin and practice of the 'Satya-Sai vow' as described in the story of the Patil in Chapter 13.

The 'Satya-Sai vow' was a devotional practice started by the grateful Patil, as detailed in Chapter 13. After being miraculously cured by Sai Baba, the Patil sought a way to express his gratitude. He adapted the traditional Hindu ritual of the Satyanarayan vow. On every Thursday, after bathing, the Patil would perform this new vow. Instead of reading the customary Satyanarayan story, he would read the three chapters dedicated to Sainath from Das Ganu's book, the 'modern Bhaktalilamrut.' The practice included the same abundance of offerings and celebration, equating Sai with Narayan and seeing no difference between them. This tradition, born from the Patil's profound experience of grace, eventually became a custom in his village.