How did Sai Baba prove to Cholkar that He was aware of Cholkar's secret act of renunciation?

Sai Baba demonstrated his omniscience to Cholkar in a deeply personal and subtle manner. After Cholkar finally arrived in Shirdi and fulfilled his vow, he was a guest at Mr. Jog's place. As Cholkar was about to leave, Baba specifically told Jog, "Give him cups of tea, well-filled with sugar." According to Chapter 15, these words were profoundly meaningful because Cholkar had secretly given up sugar, even in his tea, as a personal penance during the long delay in fulfilling his vow. Baba did not even drink tea, so His bringing it up at that precise moment, with the specific instruction for it to be "well-filled with sugar," was a clear sign to Cholkar that his secret sacrifice was known and his vow was accepted, leaving him amazed and overwhelmed with joyful tears.