To the devotees of Lord Dattatreya, Sai Baba was Datta. Once two visitors came from Goa for Baba’s darshan. Baba asked one of them for Rs. 15/- as dakshina and the man gave it. The other man volunteered to offer Rs. 35/- but Baba did not accept it. Later Shama made bold to ask him why he made such distinction between the two visitors. Baba said, “Shama, you do not know anything. I do not take anything from anyone. Musjidimai (i.e. mother musjid) calls for her debt and the debtor pays it and becomes free. Have I any home, property or family to care for, that I should need money? I require nothing. At first the man was poor and could not secure any job. He then took a vow that if he got a job he would offer his first month’s pay to Lord Datta. He soon got a job and his first month’s pay was Rs. 15/- Later he was promoted and his pay rose up to Rs.790/- p.m. But in his prosperity he cleanly forgot all about his vow. Debt, enmity and murder have got to be atoned for. The force of his karma has driven him here and I asked for the amount from him as dakshina”. The visitor in question confirmed that Baba’s words were nothing but the truth. By revealing his knowledge of his vow and the circumstances in which it was made and also demanding it Baba showed that he was Lord Datta.
About 1900, one Balasaheb Binnevala, a close relation of Nanasaheb Chandorkar, went to see Sai Baba, but only to oblige Nanasaheb. He was a worshipper of Lord Datta. When he went and saw Sai Baba, the latter appeared to him as having the three heads of Lord Data. Balasaheb was at once convinced that Sai Baba was Datta.
Source: Sai-Baba The Master from Acharya Ekkirala Bharadwaja