Dhammapada · 3.4
Sududdasaṃ sunipuṇaṃ, yatthakāmanipātinaṃ;Cittaṃ rakkhetha medhāvī, cittaṃ guttaṃ sukhāvahaṃ.
sududdasam sunipunam, yatthakama-nipatinam; cittam rakkhetha medhavi, cittam guttam sukhavaham.
Very hard to see, very subtle, alighting wherever it wishes — the mind. Let the wise guard it; a guarded mind brings happiness.
— Dhammapada 3.4
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.