I've heard that one needs permission to leave Shirdi. How is this permission granted by Sai Baba, and what role does Udi play in it?

According to the texts, departing from Shirdi requires Sai Baba's explicit permission, as transgressing this command can invite obstacles and humiliation. The process for receiving this permission is deeply connected to Udi. As described in Chapter 35, after bowing to Baba to ask for leave, the blessing he confers along with the gift of Udi Prasad is itself the permission to depart. This chapter emphasizes that no one can leave the doorstep without Baba's will, and this formal blessing with Udi signifies that his heart is pleased and the devotee is free to go.