Dhammapada · 18.5

Anupubbena medhāvī, thokaṃ thokaṃ khaṇe khaṇe;Kammāro rajatasseva, niddhame malamattano.

Anupubbena medhavi, thokam thokam khane khane; Kammaro rajatasseva, niddhame malamattano.

Gradually, little by little, moment by moment, the wise one should expel his own taints — just as a smith removes the dross from silver.

— Dhammapada 18.5

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.