Although in general the Muslims of Bengal followed the injunctions of Islaam, certain innovations and Un-Islamic practices were prevalent among them, particularly later in the period. The existence of such innovations and superstitions have too often been explained as a result of Bengal Muslims’ being mostly converts from Hindus etc who are said to have retained many of their previous Un-Islamic beliefs and practices.  Such a view is clearly superficial. A little closer look would at once show that the innovations and superstitions that are noticeable among the Muslims of Bengal were in large measure imported by the immigrant Muslims themselves, though these received further accretions from local Un-Islamic beliefs and practices. Of the innovations that definitely came along with the immigrant Muslims and that which was the most far-reaching in its effects and influence was Sufism. There is a considerable literature on the subject in various languages, and it not necessary here to enter into the academic debate as to whether Sufism grew out of European or Indian influences. Suffice to note here that Islam does not countenance asceticism and mysticism. Yet from the second century of its history these two trends made their inroads into the ranks of the Muslims and in course of time there came into being a class of mystics known as Sufis. [Source: History of The Muslims of Bengal Vol 1B page 799-800. Publisher: Imam Muhammad Bin Sa’ud University. First Edition 1406H/1985]

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Regarding Sufi Practices, the Article on this link http://www.salaficentre.com/2015/12/a-brief-acquaintance-with-the-rise-origins-and-spread-of-grave-worship-in-the-ummah-by-shaikh-shamsuddeen-al-afghaani-as-salafi-rahimahullaah/   gives a brief acquaintance with the origin of Sufi practices, such as grave worship etc