Which specific action by Sai Baba caused Kaka Mahajani's friend to forget his vow not to bow?

The pivotal event that shattered the resolve of Kaka Mahajani's friend is detailed in Chapter 35. As the friend, who had vowed not to bow, set foot on the mosque's step, Sai Baba saw him from a distance and called out, 'Why have you come in this manner?' The astonishing part was not the words, but the tone of voice Baba used. It was a perfect imitation of the friend's deceased father's vocal style. Hearing this voice, which he found 'certainly familiar,' caused the friend to melt inside and completely forget his earlier promise, leading him to spontaneously bow his head at Baba's feet.