At Varanasi, an aged Brahmin challenged Shankara's Brahma Sutra Bhashya, debating continuously for eight days. Shankara's disciple Padmapada realized through yogic insight that the challenger was actually sage Vyasa himself—the original author of the Brahma Sutras. Vyasa revealed his identity, declared that Shankara alone understood his sutras' true meaning, and blessed him with sixteen additional years of life to complete his mission. Vyasa proclaimed that Shankara's commentaries would endure until the end of the kalpa (cosmic cycle). This encounter, whether historical or hagiographical, illustrates that Shankara's interpretation became authoritative—subsequent Vedantic schools (Ramanuja's Vishishtadvaita, Madhva's Dvaita) had to define themselves in dialogue with or opposition to Shankara's Advaita framework.