What is the origin story of the name 'Sai Baba'?

The name 'Sai Baba' was bestowed upon Maharaj when he first came to Shirdi. As he entered the Khandoba temple, a resident devotee and goldsmith named Mhalasapati greeted him by saying "Aavo Sai Baba," which means "Come, Sai Baba." As Chapter 0 explains, Maharaj adopted this name for the rest of his life. When his testimony was once taken in a commission and he was asked for his name, he simply stated, "They call me Sai Baba," solidifying the identity given to him by his first devotee.