Seven minor Upanishads which have a special bearing on renunciation or Sannyasa.
Bhikṣukopaniṣad
Avadhūta Upaniṣad
Jābāla Upaniṣad
Turīyātīta Avadhūta Upaniṣad
Kaṭha Rudra Upaniṣad
Kuṇḍika Upaniṣad
Parabrahma Upaniṣad
Contains original Sanskrit text, English translation, and exhaustive notes based upon, and in the light of, the commentaries by Upanishad Brahmayogin and Swami Vivekananda.