This expression comes ultimately from Plutarch's account of Julius Caesar's decision
to divorce his wife Pompeia. The libertine Publius Clodius, who was in love with
Pompeia, smuggled himself into the house in which the women of Caesar's household
were celebrating a festival, thereby causing a scandal. Caesar refused to bring charges
against Clodius, but divorced Pompeia; when questioned he replied 'I thought my wife
ought not even to be under suspicion'.