Yoga Sutras of Patanjali translated by Yogi Kalinath - Chapter 3, Verse 8
Pada 3, Sutra 8
Tad api bahir-angam nirbeejasya
Yet these internal limbs are still external when compared to the ‘seedless’ Samadhi—Nirbija Samadhi.
The grouping of concentration (Dharana), meditation (Dhyana) and cognitive absorption (with seed—Sabija Samadhi) known collectively as Samyama still involves mind and consciousness which are subtle vehicles of Nature. Samyama takes us to the periphery of our true essence which is Atman or the Spirit Soul. In order to experience the Self as the Spirit Soul or Atman one will need to go deeper and beyond Samyama to the state known as Nirbija Samadhi.
Nirbija Samadhi is the alluded state known as Turiya in the Upanishads, the Undifferentiated state of consciousness which includes but also transcend waking, dreaming and deep sleep. In actual fact, Nirbija Samadhi is akin to deep sleep but with absolute awareness. In other words, if deep sleep is undifferentiated darkness then Nirbija Samadhi is undifferentiated illumination.