Thirukkural 298

புறள்தூய்மை நீரான் அமையும் அகந்தூய்மை வாய்மையால் காணப் படும்.

Pural tūymmai nīrān amayum akam tūymmai Vāymmaiyāl kāṇap patum

Outward purity is cleansed by water alone; inward purity is known only through truth. / External cleanliness is nothing—the purity that matters lives in truthful speech and deed.