Islam rather famously disapproves of polytheism, but I have noticed something of an overlap between Islamic and Hindu ideas, and want to know what classical Islamic scholars have concluded on the matter. Muslims and Hindus have lived together in India for centuries, and Mughal Emperors fluctuated between interfaith dialogue and intolerance. Mughal rulers even elevated Hindus to Dhimmi.
As far as I understand it, Islam emphasises strict monotheism (no God but Allah), in a way Judaism and Christianity don't. The Second Commandment doesn't deny the existence of other Gods, but rather insists that the God of Abraham must come first.
To clarify; for Muslims Allah is indivisible and absolute (tawhid), while for most Christians the trinity exists: God is father in heaven, son in Jesus, and Holy Ghost (comparable to the Holy Spirit in Judaism).
Furthermore, in the Old Testament God phrases things to imply there are other Gods or divine characters of equal status (Genesis 1:26 "Let us make mankind in our image, in our likeness"). At least, in this podcast world expert in the New Testament and early Christianity Bart Ehrman concludes as much (1h:20m... I'm not in a position to argue against someone who has studied the oldest copies of the Bible in ancient Greek and Hebrew).
Hinduism is a very broad spectrum of belief and practice, which lacks anything considered an immutable source of absolute truth, like a Torah, Bible, or Quran. However, a common foundational Hindu belief is that the nature of reality is illusionary (Maya versus Atman), and there is one absolute and ultimate creator God (Brahman). The other Gods are 'avatars', which is to say illusionary forms.
"The trimurti collapses the three gods into a single form with three faces [...] Scholars consider the doctrine of the trimurti to be an attempt to reconcile different approaches to the divine with each other and with the philosophical doctrine of ultimate reality (brahman)"
Many Hindus believe in an 'ultimate reality/truth' in the form of Brahman (easily confused with Brahma). This is said to be both the source of all existence and an unchanging absolute. Some Hindus are also practically monotheist, in the sense of worshiping Krishna as the source of all reality.
This made me wonder... given the coexistence of Muslims and Hindus in India, there must be classical scholarship by Islamic theologians on the question of how Islam and Hinduism compare with specific regards to Allah and Brahman.
What seems most curious to me, is that if Brahman is understood as a singular, absolute, and ultimate God/reality, then that is essentially Allah without (or pre?) Mohammad. This comparison must surely have been written about by some scholars, presumably most likely during the Mughal Empire.
To be clear, I am not interested in a simple definition, but an educated and technical one. I would like the cited opinions of experts who are familiar with both Islam and Hinduism.