Śivasaṃhitā 5.164

This verse unfolds one of the richest metaphors in the yogic tradition: the identification of the three great nāḍīs with the three sacred rivers of the Prayāga confluence. Iḍā is the Ganges —cool, lunar, flowing left—; piṅgalā is the Yamunā —warm, solar, flowing right—; and suṣumṇā is the Sarasvatī, the invisible river flowing between them on the subtle plane.

The historical Sarasvatī is a Vedic river that physically disappeared yet persists in tradition as an underground, invisible current. Its identification with the suṣumṇā is apt: this nāḍī too is invisible to the ordinary eye, accessible only through contemplative practice. The verb vahati («flows», active present) underscores that this current is not static but living and continuous.

The sacred geography of Prayāga —the triveni or triple confluence— is here completely internalized. The yogin need not make a pilgrimage to northern India: that place of power is carried within. This transposition from the external to the internal is one of the most characteristic movements of Tantrism and haṭhayoga, and the Śivasaṃhitā executes it here with remarkable economy and elegance.