Dhammapada · 5.4

Yo bālo maññati bālyaṃ, paṇḍito vāpi tena so;Bālo ca paṇḍitamānī, sa ve bāloti vuccati.

Yo balo mannati balyam, pandito vapi tena so; Balo ca panditamani, sa ve baloti vuccati.

A fool who knows he is a fool is, by that very knowing, already wise. But a fool who imagines himself wise is truly a fool.

— Dhammapada 5.4

Source: Pali text from the Khuddaka Nikāya of the Pali Canon (oldest extant Buddhist scripture, compiled c. 3rd century BCE). Public-domain English readings drawn from F. Max Müller's translation in Sacred Books of the East, Vol X (1881) and the Buddhist Publication Society's freely-licensed Acharya Buddharakkhita rendering.