On 28 September 1835 (or according to many others 1838) Shirdi Sai Baba was born to Gangabhavadya and Devagiriamma, a ferryman and his wife. In the book "Seven days Shirdi Sai’, the biography of Shirdi Sai Baba in Dutch, in chapter 1 is told how Shiva and Parvati come to test the dedication of Devagiriamma and then bless her.
Below is an excerpt from that chapter:
' The old man and the newly arrived woman were none other than the divine couple Mother Parvati and Lord Shiva. Shiva said: ‘Parvati, fulfill the deepest desires of this woman,' to which Parvati replied: 'You are the Supreme. Please let your grace descend upon her.' But Shiva said: 'I came to test her, you came in answer to her prayers. Therefore, it is up to you to bless her. '
Again there was a knock on the door. This time Devagiriamma opened the door without trepidation, because there was another woman present. Before her stood Mother Parvati and Lord Shiva in their divine appearance. She could not contain her joy and knelt at their feet. Parvati said: 'My child, Shiva came to test you. I have come in response to your prayers. Therefore ask me for any grace and I'll grant it to you.' Devagiriamma was so overjoyed that she couldn't think of anything to ask, so the goddess Parvati blessed her and said,: 'My child, you have everything in your life except children. Therefore, I will give you a son who will bring honor to your line and a daughter too, so you can build up good karma by giving her away in marriage.' Shiva added,: 'Mother, I am very pleased with your devotion. I myself will be born as your third child.' And even before Devagiriamma could get up, the divine couple disappeared. –narrated by Sathya Sai Baba-
Eventually Devagiriamma would indeed give birth to three children, and the third is the one that later becomes known as Sai Baba of Shirdi. In a speech at Gurupurnima in the year 1963 Sathya Sai Baba told that this happened as a result of the promise that Shiva and Parvati had given thousands of years earlier to Sage Bharawaja:
'At the most appropriate time Bharadwaja held the ritual blessing under Shakti's supervision, and after its completion Shiva and Shakti were so pleased that they gave away more favors to the sage. Shiva promised him that they would both take the human form and would be born in the Bharadwaja line thrice: Shiva alone as Shirdi Sai Baba, Shiva and Shakti together in Puttaparthi as Sathya Sai Baba, and later Shakti alone as Prema Sai Baba.’
(also to be found in ‘Zeven dagen Shirdi Sai‘)
Read more about the birth date of Shirdi Sai Baba in this post.