Nibbana (Pali) or nirvana (Sanskrit) is the asankhata-dhatu (unconditioned element), the cessation (nirodha) of the three fires — raga, dvesa, and moha — constituting the Third Noble Truth as proclaimed at Sarnath. The Udana (8.3) preserves the Buddha's description: 'There is, bhikkhus, that ayatana where there is neither pathavi, nor apo, nor tejo, nor vayo' — a formulation that places nibbana beyond all conditioned categories. The Theravada Abhidhamma classifies nibbana as the sole asankhata dhamma (unconditioned reality) among its entire taxonomy of dhammas. Nagarjuna's Mulamadhyamakakarika (chapter 25) radicalized the concept by demonstrating that samsara and nirvana are not ontologically distinct — 'there is not the slightest difference between samsara and nirvana' — since both are empty of svabhava, and the realization of this non-difference is itself liberation.