Abdul Baha after reading a letter of one of Baha’i regarding Hindus said :

You have written concerning the statements of certain Hindus.

Exalted is God! (*Used as a note of exclamation.*) What speech is that and what an idea and supposition whose error is obvious! In the world of humanity, certain personages appeared who became the trainers of the world, shone forth like unto the sun, were adorned by the people of all religions, became recipients of Divine Revelations and dawning places of the light of Truth. Consider, therefore, the human temple, and see to what heights of loftiness and exaltation it has reached!

On the other hand, many exist as human beings who are adorers end worshipers of stone and clay, that is, the mineral, which is the lowest of beings. Consider how base and low are they when their object of worship is the basest of things, such as stone, clay and mineral!

How then can one compare the two above classes of human beings with each other? No, by God, this were a great calamity! The outward is the expression of the inward. In the different species and classes of beings, none that progresses can reach the station of a higher being. For instance, no matter how much the mineral may progress, it will not attain the virtue of growth in its mineral world. Likewise the vegetable, no matter how much it may progress and develop in the vegetable world, it will never attain sense-perception. Similarly the animal, no matter how much training it may receive or make progress, it can not attain the rational faculty.

Source : 1906 Pilgrim Notes of Ali Kuli Khan

Shoghi Effendi, First Baha’i Guardian said:

…The origins of this (Hinduism) and many other religions that abound in India are not quite known to us, and even the Orientalists and the students of religions are not in complete accord about the results of their investigations in that field. The Bahá’í writings also do not refer specifically to any of these forms of religion current in India. So, the Guardian feels it impossible to give you any definite and detailed information on that subject. He would urge you, however, to carry on your studies in that field, although its immensity is well-nigh bewildering, with the view of bringing the Message to the Hindus….

From a letter written on behalf of Shoghi Effendi: Dawn of a New Day, p. 198