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

Sai Baba provided a miraculous and undeniable sign to show Cholkar he was aware of his secret vow. After Cholkar finally arrived in Shirdi, had darshan, and fulfilled his promise, he was a guest of another devotee named Jog. As Cholkar was about to leave, Baba specifically instructed Jog, "Give him cups of tea, well-filled with sugar." Chapter 15 explains that this was deeply meaningful because Baba himself did not drink tea, and more importantly, Cholkar had secretly given up sugar entirely as a personal penance during the long delay in fulfilling his vow. This specific command was a direct acknowledgment of Cholkar's private sacrifice, confirming Baba's omniscience.