How did Sai Baba prove to Cholkar that he knew about his secret vow and personal sacrifice?

Sai Baba demonstrated his omniscience to Cholkar in a subtle yet powerful manner. As explained in Chapter 15, after Cholkar had made his vow to distribute sugar upon passing an exam, he was forced to delay his trip to Shirdi due to poverty. During this time, he secretly gave up sugar as a personal sacrifice. When Cholkar finally arrived in Shirdi and fulfilled his vow, he was a guest at Jog's place. As he was leaving, Baba instructed Jog, "Give him cups of tea, well-filled with sugar." Since Baba did not drink tea himself, this specific instruction at that exact moment was a clear sign. It showed Cholkar that Baba knew not only about the original vow involving sugar but also about his secret, personal penance of abstaining from it, which left Cholkar amazed and filled with tears of joy.