Solon Quote

Watch well each separate citizen,
Lest having in his heart of hearts
A secret spear, one still may come
Saluting you with cheerful face,
And utter with a double tongue
The feigned good wishes of his wary mind.

Diogenes Laërtius (trans. C. D. Yonge) The Lives and Opinions of Eminent Philosophers (1853), "Solon", sect. 13, p. 29.