Al-biruni perceives a significant difference between hindus and muslims in

In religious beliefs and practices.
According to Al-biruni, the hindu's worship several Gods while the muslims only worship one God in monotheistic manners.
Al-Boruni also believe the concept of religion perception of Hindu between lower class and upper class society are different due to infairness in the social structure while for Muslims it's generally the same.

Al-biruni saw Hindus and Muslims as complete opposites. They differed in language, customs, religions, and manners. He studied without bias, and was therefore able to see that the hatred of Hindus was due to a lack of understanding of different values.