na hy ekasmād guror jñānaṁ susthiraṁ syāt supuṣkalam
na hy ekasmād guror jñānaṁ susthiraṁ syāt supuṣkalam |
brahmaitad advitīyaṁ vai gīyate bahudha rṣibhiḥ ||
(Śrīmad Bhāgavatam: 11.9.31)
“Indeed knowledge [received] from one guru shall not become sufficiently steady and sufficiently extensive. This nondual Brahman is sung of by seers in numerous ways.”