Can you explain the vow Cholkar made to Sai Baba and how Baba proved he knew about it?

Cholkar, facing a critical examination for his job, made a vow to Sai Baba. As described in Chapter 15, he promised that if he passed, he would visit Baba's feet in Shirdi and distribute sugar candy (khadisakhar). After his wish was granted, he was delayed in fulfilling the vow due to financial struggles. As a personal penance, he gave up sugar entirely. When he finally reached Shirdi and fulfilled his vow, Baba instructed a host to give Cholkar "cups of tea, well-filled with sugar." This specific instruction amazed Cholkar, as it proved Baba was omniscient and aware of his secret, personal renunciation of sugar, thereby confirming his faith.