Infinity, eternity, countlessness in Buddhism I'm interested in concepts of infinity, eternity, countlessness, etc. in Buddhist thought.

Could you please help me out with sources, both primary and secondary, where these concepts are used?

I know that there are countless beings, that the world existed forever, that Buddha's knowledge is limitless, that there are countless Buddhas, countless universes. But it is extremely hard to pin down exact scriptures where these concepts are elaborated and to find secondary sources where the issues of infinity and eternity are discussed.

Will be grateful for any help.

Thanks!
Questions regarding eternity are considered to lack an answer:
https://www.wisdomlib.org/definition/avyakrita
According to the sutta quoted below, Buddha refrained from answering that type of questions. The reason for this comes from the buddhist notion of anatta, also mentioned below. The concepts are a bit hard to untangle, but this is the gist of it:

How is it, Master Gotama, is the world eternal?”… as above …
“What, Master Gotama, is the cause and reason why, when wanderers of other sects are asked such questions, they give such answers as: ‘The world is eternal’ … or ‘The Tathagata neither exists nor does not exist after death.’ And what is the cause and reason why, when Master Gotama is asked such questions, he does not give such answers?”
“Vaccha, wanderers of other sects regard form as self, or self as possessing form, or form as in self, or self as in form. They regard feeling as self … perception as self … volitional formations as self … consciousness as self, or self as possessing consciousness, or consciousness as in self, or self as in consciousness. Therefore, when the wanderers of other sects are asked such questions, they give such answers as: ‘The world is eternal’ … or ‘The Tathagata neither exists nor does not exist after death.’ But, Vaccha, the Tathagata, the Arahant, the Perfectly Enlightened One, does not regard form as self … or self as in consciousness. Therefore, when the Tathagata is asked such questions, he does not give such answers.

https://suttacentral.net/sn44.8/en/bodhi