Can you tell me the story of Cholkar's vow to Sai Baba?

The story of Cholkar, detailed in Chapter 15, is a touching account of faith. Cholkar, facing a critical job examination, vowed to distribute sugar candy in Sai Baba's name if he passed. After his wish was granted, financial hardship delayed his trip to Shirdi. As a personal penance during this delay, Cholkar gave up eating sugar entirely, even drinking his tea without it. When he finally reached Shirdi and fulfilled his vow, Baba demonstrated his omniscience by telling another devotee to give Cholkar tea 'well-filled with sugar,' proving that Cholkar's secret sacrifice was known to him all along.