How did Sai Baba obtain the wood for his Dhuni, and what was the specific role of Udi in a devotee's departure from Shirdi?

Chapter 33 of the Sai Satcharitra details that Sai Baba would buy firewood bundles from those who had a surplus, piling up the logs to be used in his sacred fire, the Dhuni. The ash from this fire became the Udi he distributed. This chapter also clarifies the role of Udi in travel. When devotees asked for permission to leave Shirdi, Baba giving them Udi was the established practice and was considered the true confirmation that permission was granted. This act would make the devotee feel enthusiastic about their journey home.