Where did Easwaran get his Dhyanas?

Jhanas, called by Easwaran by their sanskrit name dhyanas, are centrally important to Buddhism. They are, arguably (of course), the original invention of the Buddha that makes Enlightenment possible. So my question is: Where did Easwaran get his conception of the jhanas?

There are a million and one doctrinal disputes about everything in Buddhism, but there are things that are generally accepted that Easwaran ignored. While 'jhana' is the Buddha's preferred word to use for what we call 'meditation' the jhanas are a series of refined states possible in meditation, the four jhanas are not the four levels of mediation. I've also never seen his description of what it is like to experience those states anywhere else.

I suppose I would just be happy if he told us what his canonical source he referenced, teacher he learned from, or else why he synthesized his understanding of the Dhamma in this way.