The engagements of the Great Souls, freed from delusion and perfect in their realization of God, are described here: "Satatam kirtayanto mam"—they are always (satatam) chanting (kirtayanto) My glories, and "nitya-yukta upasate"—always worshiping Me.
So I do not know how you can say "indisputable." And, if you want reference from the Vedas, I can give you many. In the Vedas the chief transcendental vibration Omkara is also Krishna. Pranaba Omkara is the divine substance of the Vedas. Following the Vedas means chanting the Vedic Mantras, and no Vedic Mantra is complete without Omkara. In the Mandukya Upanisad, Omkara is stated to be the most auspicious sound representation of the Supreme Lord. This is also confirmed again in the Atharva Veda. Omkara is the sound representation of the Supreme Lord and is therefore the principal word in the Vedas. In this connection, the Supreme Lord Krishna says, "Pranaba Sarva Vedesu" (B.G. 7:8)—"I am the syllable Om in all the Vedic Mantras."
Furthermore, in the 15th verse of chapter 15, Bhagavad-gita, Krishna says, "I am seated in everyone's heart. By all the Vedas I am to be known; I am the Compiler of Vedanta and I know Veda as it is." The Supreme Lord, seated in everyone's heart, is described in both the Mundaka and Svetasvetara Upanisads; "Dwa suparna sayuja sakhaya . ." The Supreme Lord and the individual spirit soul are sitting in the body as two friendly birds in a tree. The one bird is eating the fruits of the tree or reactions of material activities and the other bird, the Supersoul, is witnessing.
The goal of Vedantic study, therefore, is to know the Supreme Lord Krishna. This point is stressed in Bhagavad-gita chapter 8, verse 13, where it is stated that by the mystic yoga process, ultimately vibrating the sacred syllable Om, one attains to His Supreme Spiritual Planet. In the Vedanta Sutras, which you have certainly read, the fourth chapter, fourth Adhikaran twenty-second Sutra states it positively; "Anavritti sabat . . ."—By sound vibration one becomes liberated. By devotional service, by understanding well what is the Supreme Personality of Godhead, anyone who goes to His Abode never comes back again to this material condition. How is it possible? The answer is, simply by chanting His name constantly.