It is well-known that Baba took Dakshina from all, and out of the amount thus collected, He spent a lot on charity and purchased fuel with the balance left with Him. This fuel he threw in the Dhuni - the sacred fire, which he kept ever burning. The ash from this fire was called Udi and it was freely distributed to the devotees at the time of their departure from Shirdi. Udi or ash is the purest substance on earth having tremendous powers of doing and undoing and is the result of sacrifices offered to fire (agni) which purifies everything by destroying whatever is evil.
Performing 'Yagha' (Dhuni) is the most pious ritual recommended in the ancient Vedic literature.
There is a deeper underlying significance behind Baba's practice of distributing Udi. Baba taught by his Udi that all the visible phenomena in the universe are as transient as the ash. So much about the spiritual implication of Udi. It had also its material significance. It conferred health, prosperity, freedom from anxiety and many other worldly gains.So the Udi has helped us to gain both our ends - MATERIAL as well as SPIRITUAL.