Abdul's Notebook:
The key to Marianne Warren's research into Sai Baba's Islamic roots was finding Abdul's notebook. Abdul was one of Sai Baba's closest disciples, and took care of Sai Baba's dergah after his death. To those unfamiliar with Shirdi Sai Baba, one might wonder why this is so important, and why it connects with what the Islam in India class has been about.
After his death, Sai Baba has been treated as a avatar, and now as a deity, with statues all around the world.
The issue not that he has been embraced by the Hindu population, but that he has been forgotten by Muslims as a faqir, which he always called himself.
After Sai Baba's death, his dergah was treated like a traditional Muslim center, not unique in that it encompasses Hindus as well, since many Mazars and dergahs attract all people in India. After many years of Abdul managing the tomb, a wealthy Hindu Patron visited it, and believed that it was not being taken care of "properly". He then appealed to the government, and had Abdul taken out of his position. During this time, the small picture was replaced with a statue, a giant "Om" sign was put over "shree sai baba" written in english. Abdul was allowed to return in an honorary position for his last few years of life, though since that time, just naturally as his followers were more Hindu than Muslim, the Muslim side of Sai Baba has been eclipsed.
That is what makes the discovered notebook of teachings so fascinating. It completely recontextualizes him as a learned Muslim, though with a very broad minded philosophy that sees all religions as a part of one vast truth, though he himself was rooted in Islam.
The notebook contains detailed Islamic teachings, including poetry, Qur'anic suras, hadith, lists of silsilas of many Sufi orders, lists of early Islamic figures such as the caliphs, Prophet's family etc.
Here are some interesting passages that show his unique position as a Sufi teacher:

"In the name of Allah the most beneficent the most merciful.
Religious emotion in full is purely spiritual. It is not material. Secondly it means that you will see the world as material or as only relatively real (until you have a vision of God). Parvardigar! O Dear One!, Oh Dear One! the material (relative state) world is unreal. There is no place for intellect and inference. Those who regard the spirit as without begining, this is not true. It is wrong to address the spirit because it is dependent on others. The real form of man is prana- life force."
(Warren 279)

"When in the nimbar (niche) of your heart, the Beloved is enthroned, what is the need for the pesh-iman (priest)? If we can achieve ivadat (our end) by prayer to God (Allah), what is the necessity to go to the masjid to listen to the khutba? If all the time we are engrossed in devotion to God, why should be we namaz five times a day, in the morning, noon etc. ? If we are all in love with the Beloved, we will go and reside in the mandir- why should we go to and visit the Ka'ba in Mecca?"
(Warren 302)

"Vishnu is equal to the Bismillah ar-Rahim, Allah the Merciful the Pardoner. Ali is equal to Brahma. Mahadec is equal to Mohammaed and to Malik al-maut, the angel of death"

"O Lighthouse of widom! the helper [of the helpless]!
O purifier of the self!, O Lord of the two worlds!
O Merciful Allah! Head of the Believers! [Hazrat Mohammed]
Abu Talib's son is the Lion of Allah! Powerful Ali!
Hazrat Imam Hasan! Hazrat Imam Husain!
The first Mehdi and the last Mehdi [the saviour yet to come]
There is no other God but Allah and Mohammed is his messenger."
(Warren 308)

One one can see, Sai Baba was a Muslim, though could be considered a heterodox one. His teachings bring both Islamic and Hindu teachings together. When speaking to Abdul, his language was Islamic, though stressed the truth of Hinduism as well.
Said Baba did a Dhikr of the name of Allah his whole life, but told his Hindu disciplies to repeat "Ram, Krishna" or other Hindu holy names.
Sai Baba of Shirdi's life was about bringing together the religious communities and rejecting hatred of any kind. It is said that some of his Hindu disciples from learned or high backgrounds though it below them to honor a Sufi. One person had a vision of the Hindu deity they worshipped with such love sitting where Sai Baba was. This was later explained as a teaching tool, so that one would not think themselves above or below anyone.