I heard a story about someone using incense ash for a scorpion sting because they couldn't find Udi. Can you tell me more about that?

Yes, Chapter 33 narrates this remarkable incident. A friend of the devotee Narayanrao was stung by a scorpion and was in severe agony. When they went to find Sai Baba's Udi to apply to the sting, they could not locate it. In that moment of crisis, Narayanrao prayed compassionately to a picture of Baba's image. He then noticed the ash from burnt incense sticks that had fallen at the bottom of the picture frame. As Chapter 33 explains, he considered this ash to be Udi, took a pinch, and applied it to the sting while chanting Sai's name. The effect was immediate; the pain subsided completely, demonstrating the immense power of faith.