Jaratkarava Artabhaga

One of the sage Yajnavalkya’s interviewers in the Brhadaranyaka Upanishad,
one of the earliest of the Upanishads.
The third chapter of this upanishad
presents a series of questioners, each
trying to test Yajnavalkya’s assertion that
he is the best brahmin of all. Artabhaga
finally questions Yajnavalkya about the
human sense faculties and their realms
of action, and eventually asks what happens to a person after death. Yajnavalkya
draws him aside in private, and talks to
him about karma (“action”), in what
is generally regarded as the oldest
reference to this fundamental Indian
religious idea.