Jabala Upanishad has complete details/concepts about four Ashramas.

Upanishad:

• The literal meaning of Upanishad is to sit near someone.
• There are 108 Upanishads, of which 13 are the most prominent.
• The Upanishads dwell on the Atman and Brahman, and focus a lot on the philosophy about life, universe, self, body, sacrifice, etc.
• They emphasise that the knowledge of the self or atman should be acquired and that the relation of the atman with the Brahman should be properly understood.
  • Chhandogya Upanishad: First three ashramas (Brahmacharya, Garhasthya, Vanaprastha).
  • Brahadarankya Upanishad: Samsara (transmigration of soul).
  • Jabala Upanishad: Four ashrams (Brahmacharya, Garhasthya, Vanaprastha, Sannyas).