As is in Shri Sai Satcharita, by Hemadpant .. Chapter I Page 3

Om Sai Shri Sai Jaya Jaya Sai

Sai Baba lived in Shiridi for about sixty years and during this long period, He did the business of grinding almost every day - not, however, the wheat alone; but the sins, the mental and physical afflictions and the miseries of His innumerable devotees.  The two stones of His mill consisted of Karma and Bhakti, the former being the lower and the latter the upper one.  The handle with which Baba worked the mill consisted of Jnana.  It was the firm conviction of Baba that knowledge or Self-realization is not possible, unless there is the prior act of grinding of all our impulses, desires, sins; and of the three gunas, viz. Sattva, Raja and Tama; and the Ahamkara, which is so subtle and therefore so difficult to be got rid of.

Bow to Shri Sai - Peace be to all