Yoga Sutras of Patanjali · 4.21

चित्तान्तरदृश्ये बुद्धिबुद्धेरतिप्रसङ्गः स्मृतिसंकरश्च॥२१॥

cittāntaradṛśye buddhibuddher atiprasaṅgaḥ smṛtisaṅkaraś ca

If the mind were known by another mind, there would be an infinite regress of cognitions of cognition, and memory would be confused.

— Yoga Sutras of Patanjali 4.21

Source: Sanskrit attributed to Patanjali (c. 2nd century BCE – 4th century CE). Public-domain English readings drawn from Swami Vivekananda's 'Raja Yoga' (1896) and Charles Johnston's 'The Yoga Sutras of Patanjali' (1912).