In his book, "Pakistan or the Partition of India", towards the end of Chapter 4, Ambedkar writes,
"The Muslim invaders, no doubt, came to India singing a hymn of hate against the Hindus. … Its (Islam's) growth is so thick in Northern India that the remnants of Hindu and Buddhist culture are just shrubs. Even the Sikh axe could not fell this oak. Sikhs, no doubt , became the political masters of Northern India, but they did not gain back Northern India to that spiritual and cultural unity by which it was bound to the rest of India before HsuanTsang."
It is interesting to note that despite his views on casteism in Hinduism, Ambedkar saw Hinduism, Buddhism and Sikhism as ONE Indian culture, at the same time, categorically calling Islam an alien culture. In chapter 6 of the same book, he writes,
"From a spiritual point of view, Hindus and Musalmans are not merely two classes or two sects such as Protestants and Catholics or Shaivas and Vaishnavas. They are two distinct species... For them Divinity is divided and with the division of Divinity their humanity is divided and with the division of humanity they must remain divided. There is nothing to bring them in one bosom."
Ambedkar had unequivocally advocated for a population exchange in case of division. Hindus and Sikhs from Pakistan come to India, and Muslims from India, got to Pakistan. In fact, both Sawarkar and RSS were trying to keep India undivided, but Ambedkar, had other views which he articulated in Chapter 6 of the same book. Some of these observations can be in sync with the reality today.
"That the transfer of minorities is the only lasting remedy for communal peace is beyond doubt. .. there is no reason to suppose that what they did cannot be accomplished by Indians. After all, the population involved is inconsiderable and because some obstacles require to be removed, it would be the height of folly to give up so sure a way to communal peace... The only way to make Hindustan homogeneous is to arrange for exchange of population. Until that is done, it must be admitted that even with the creation of Pakistan, the problem of majority vs. minority will remain in Hindustan as before and will continue to produce disharmony in the body politic of Hindustan."
Ambedkar, in the same book, has severely criticized Gandhi for his duplicity and double standards he adopted on Hindu killings v/s muslim killings. He writes-
"But Mr. Gandhi has never protested against such murders. Not only have the Musalmans not condemned these outrages but even Mr. Gandhi has never called upon the leading Muslims to condemn them. He has kept silent over them. Such an attitude can be explained only on the ground that Mr. Gandhi was anxious to preserve Hindu-Moslem unity and did not mind the murders of a few Hindus, if it could be achieved by sacrificing their lives. This attitude to excuse the Muslims any wrong, lest it should injure the cause of unity, is well illustrated by what Mr. Gandhi had to say in the matter of the Mopla riots. The blood-curdling atrocities committed by the Moplas in Malabar against the Hindus were indescribable. All over Southern India, a wave of horrified feeling had spread among the Hindus of every shade of opinion, which was intensified when certain Khilafat leaders were so misguided as to pass resolutions of " congratulations to the Moplas on the brave fight they were conducting for the sake of religion". Any person could have said that this was too heavy a price for Hindu-Moslem unity. But Mr. Gandhi was so much obsessed by the necessity of establishing Hindu-Moslem unity that he was prepared to make light of the doings of the Moplas and the Khilafats who were congratulating them. He spoke of the Moplas as the "brave God-fearing Moplas who were fighting for what they consider as religion and in a manner which they consider as religious ".
And, while Ambedkar later renounced Hinduism due to caste system, he has elaborated how Islam too had an elaborate caste system (again in practice, even though Quran speaks against any division in Islam as an evil).
"Islam speaks of brotherhood. Everybody infers that Islam must be free from slavery and caste. Regarding slavery nothing needs to be said. It stands abolished now by law. But while it existed much of its support was derived from Islam and Islamic countries… The existence of these evils among the Muslims is distressing enough. But far more distressing is the fact that there is no organized movement of social reform among the Musalmans of India on a scale sufficient to bring about their eradication. The Hindus have their social evils. But there is this relieving feature about them—namely, that some of them are conscious of their existence and a few of them are actively agitating for their removal. The Muslims, on the other hand, do not realize that they are evils and consequently do not agitate for their removal. Indeed, they oppose any change in their existing practices.
It is noteworthy that the "Muslims opposed the Child-Marriage Bill brought in the Central Assembly in 1930, whereby the age for marriage of a girl was raised to 14 and of a boy to 18 on the ground that it was opposed to the Muslim canon law. Not only did they oppose the bill at every stage but that when it became law they started a campaign of Civil Disobedience against that Act. Fortunately the Civil Disobedience campaign of the Muslims against the Act did not swell and was submerged in the Congress Civil Disobedience campaign which synchronized with it. But the campaign only proves how strongly the Muslims are opposed to social reform."
He further writes, "Having been taught that outside Islam there can be no safety; outside its law no truth and outside its spiritual message there is no happiness, the Muslim has become incapable of conceiving any other condition than his own, any other mode of thought than the Islamic thought. He firmly believes that he has arrived at an unequalled pitch of perfection; that he is the sole possessor of true faith, of the true doctrine, the true wisdom ; that he alone is in possession of the truth—no relative truth subject to revision, but absolute truth."
And, Ambedkar also writes, "The third thing that is noticeable is the adoption by the Muslims of the gangster's method in politics. The riots are a sufficient indication that gangsterism has become a settled part of their strategy in politics. .. So long as the Muslims were the aggressors, the Hindus were passive, and in the conflict they suffered more than the Muslims did. But this is no longer true. The Hindus have learned to retaliate and no longer feel any compunction in knifing a Musalman. This spirit of retaliation bids fair to produce the ugly spectacle of gangsterism against gangsterism."
In chapter 12, he observes, "Among the tenets one that calls for notice is the tenet of Islam which says that in a country which is not under Muslim rule wherever there is a conflict between Muslim law and the law of the land, the former must prevail over the latter and a Muslim will be justified in obeying the Muslim law and defying the law of the land."
"Islam is a close corporation and the distinction that it makes between Muslims and non-Muslims is a very real, very positive and very alienating distinction. The brotherhood of Islam is not the universal brotherhood of man. It is brotherhood of Muslims for Muslims only. There is a fraternity but its benefit is confined to those within that corporation. For those who are outside the corporation, there is nothing but contempt and enmity. ...
In other words, Islam can never allow a true Muslim to adopt India as his motherland and regard a Hindu as his kith and kin. That is probably the reason why Maulana Mahomed Ali, a great Indian but a true Muslim, preferred to be buried in Jerusalem rather than in India."
It is for the Muslim scholars to rebut or validate what Ambedkar has written about Islam. But, the secular politicians, who invoke Ambedkar in everything relating to Dalit politics, and have formed a Dalit-Muslim alliance, should also clarify if they agree to what Ambedkar has written.