Ignorance is the worst stain of all.

Tato malā malataraṃ, avijjā paramaṃ malaṃ;

Etaṃ malaṃ pahantvāna, nimmalā hotha bhikkhavo.

Ignorance is the worst stain of all. 

Let the Bhikkhu remove ignorance and be clean.

Dhammapada, 243.