This comes from his first great legal victory. Cicero prosecuted Gaius Verres for crimes he committed while governor of Sicily. Theft of artworks, unlawful detention and execution of Roman citizens. The crimes were numerous and heinous. The biggest hurdle facing Cicero in his prosecution of Verres was that the ill gotten gains had been used quite liberally as bribes in the case. The jury was composed of Senators and the defense counsels were Hortensius and Metellus Pius who, at the time, were both consul-elect.I highly recommend reading the entire post. It may well inspire you to pull a few history books of the shelf for a little reacquainting session.
Knowing that there was a very limited time for the trial (if it progressed into the new administration there would be no chance at all of a conviction) Cicero rose on the first day of court and said this:
"Gentlemen of the court, at this great political crisis there has been offered to you, not through man's wisdom but almost as the direct gift of heaven, the very thing you most need---a thing that will help more than anything else to mitigate the unpopularity of your Order and the suspicion surrounding these courts. A belief has become established---as harmful to the republic as it is to yourselves---that these courts, with your senators as the jury, will never convict any man, however guilty, if he has sufficient money.
But the character of the many I am prosecuting, is such that you may use him to restore your own good name. Gaius Verres has robbed the Treasury and behaved like a pirate and a destroying pestilence in his province of Sicily. You have only to find this man guilty, and respect in you will be rightly restored. But it you do not---if his immense wealth is sufficient to shatter your honesty---well then, I shall achieve one thing at least. The nation will not believe Verres to be right and me wrong---but they will certainly know all they need to know about a jury of Roman Senators!"
Also at Ezra's place.