The Buddha explains his journey before the enlightenment in Ariyapariyesanasutta where he explains how he learned from Āḷāra Kālāma and Uddaka Rāmaputta. He learned arūpa jhānas from these two teachers. There are other suttas that mention people who achieved jhānas with paṭhavi, āpo, etc. Currently it appears that there is no other tradition or a religion that explains jhānas and their nature otherthan Buddhism.
Eventhough Hinduism and Upanishads discuss about meditation I could not find any discriptions about the characteristics of jhānas. They have explainations about samādhi and vipassana; are different from Buddhist teachings. Some people argue the Buddha adopted the path from Upanishads and such teachings which is doubtful where no poper discriptions about jhānas found in those teachings.
The Buddha takes up some of the thoughts of the Upanisads and gives to them a new orientation. The Buddha is not so much formulating a new scheme of metaphysics and morals as rediscovering an old norm and adapting it to the new conditions of thought and life (Radhakrishnan, 1957)
Radhakrishnan’s opinion is somewhat true because the Buddha gave new definitions to some teachings which were already there. In some occations the Buddha showed the right way to find what they are looking for.
But when it comes to the path to nibbāna (nirvāna) it is the Buddha who formulated the practice as he explained to the group of five ascetics in SN 56.11 where the Buddha says four noble truths were not learned before (pubbe ananussutesu dhammesu). And this is confirmed in Cūḷasīhanādasutta where the Buddha says there are no true ascetics in other sects (suññā parappavādā samaṇebhi aññehīti).
If there are no details about jhānas in Upanishads and other scriptures it is reasonable to assume that teachers who practiced and tought meditation to achieve jhānas are independent from the main stream.
Are there teachings other than Buddhism which explains jhānas (Dhyānas) ?
If not what may be the reason?