Can you tell me the full story of Cholkar, his vow, and how Sai Baba revealed His omniscience?

The story of Cholkar, detailed in Chapter 15, is a profound example of faith and Sai Baba's all-knowing nature. Cholkar, facing financial hardship, vowed that if he passed an important examination to secure his job, he would visit Shirdi and distribute sugar candy (khadisakhar). He passed by Baba's grace but was too poor to afford the journey immediately. As a personal penance during this delay, he gave up sugar completely. When he finally reached Shirdi and fulfilled his vow, Baba instructed another devotee, Jog, to give Cholkar tea that was 'well-filled with sugar.' This astonished Cholkar, as it proved Baba knew his secret vow and the personal sacrifice he had made, confirming Baba's omnipresence and loving care for his devotees.