“Poison cures in certain contingencies, and in those cases poison is not an evil thing.”
Jean-Louis Guez de Balzac (1597–1654) French author, best known for his epistolary essays
Le venin guerit en quelque rencontre, et, ce cas-là, le venin n'est pas mauvais.
Aristippe, ou De la cour (1658), Discours VI.
Translation reported in Harbottle's Dictionary of quotations French and Italian (1904), p. 139.