If you wash a donkey in a sacred stream, it will not turn to an Arab steed; even so, whatever advice you offer a scoundrel, you cannot purify his mind. You may feed a snake on sugar and nectar, but the poison within it will not vanish. Tuka says, If you offer a dog milk, it is all the same to him as vomit.
Hinduism
Tukaram, Poem 997
Source The Poems of Tukârâma, trad. J. Nelson Fraser et K. B. Marathe, 3 vol., 1909-1915, archive.org · Contents