For one who calls himself guardian of the many, as the wise say, should first be guardian of himself.

[Qui multorum custodem se profiteatur, eum sapientes sui primum capitis aiunt custodem esse oportere.]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

Philippics [Philippicae; Antonian Orations], No. 12, ch. 10 / sec. 25 (12.10/12.25) (43-03 BC) [tr. Wiseman]
    (Source)

On the death of Gaius Trebonius in January, 43 BC, one of the conspirators in Julius Caesar's assassination, who was captured and executed by Dolabella.

(Source (Latin)). Other translations:

The wise say that he to whose care the safety of many is entrusted must first show that he can take care of himself. [ed. Harbottle (1897)]

In truth, a man who professes to be himself a defender of many men, wise men say, ought in the first place to show himself able to protect his own life. [tr. Yonge (1903)]

Wise men say that he who professes to be the guard of many should first of all be the guard of his own life. [tr. Ker (Loeb) (1926)]