(Srila Prabhupada preaching at Conway Hall, London, 1969)
"Ācāryas will never say, 'I think.' 'It is in my opinion.' No. Such things are not accepted. No personal opinion. It must be supported by Vedic evidences. That is called paramparā system, genuine system of understanding. As Kṛṣṇa says, evaṁ paramparā-prāptam imaṁ rājarṣayo viduḥ (BG 4.2). No change. Therefore we are presenting Bhagavad-gītā as it is. We do not change. We have no power to change. Then where is the authority of Bhagavad-gītā? I am a third-class man, and if I change the statements in the Bhagavad-gītā, then where is the authority of Bhagavad-gītā? That is going on."
(Srila Prabhupada Lecture, Vrindavan, October 22, 1972)