How did Sai Baba manage to light the lamps in the mosque when the shopkeepers wouldn't give him any oil?

This story describes a well-known miracle of Sai Baba. According to Chapter 5, Baba had a great fondness for lighting lamps and would daily ask local shopkeepers for oil. The merchants grew tired of this and conspired to refuse him. When they did, Baba returned to the mosque, took a tin pot with a tiny bit of oil, poured water into it, and drank it as an offering. He then filled the lamps with plain water, and upon lighting them, they miraculously burned all night. This event left the grocers astonished and repentant for having lied to him and doubting his power.