What is the 'Satya-Sai vow' described in Chapter 13, and how did this tradition begin?

The 'Satya-Sai vow' was a tradition started by the Patil after he was miraculously cured of his disease by Sai Baba's grace. As detailed in Chapter 13, the Patil was inspired by the common practice of vowing to perform a Satyanarayan puja to overcome a crisis. He adapted this by creating the Satya-Sai vow, which he would perform every Thursday. Instead of reading the Satyanarayan story, the Patil would read the three chapters about Sainath from Das Ganu's 'Bhaktalilamrut.' He saw no difference between Narayan and Sai, and this practice of devotion, complete with offerings, brought him immense peace and eventually became a custom in his village.