Kaivalya Upaniṣad 11

This episode describes the four stages of āśramas; Brahmacharya (student), Gṛhastha (householder), Vanaprastha (forest dweller), and Saṅyāsa (renunciate). It also elucidates the difference between and the reason for meditating upon Saguna Brahman (with form) and contemplating on Nirguṇa Brahman (without form).