Plutarch, The Life of Cato the Younger 8

When the Servile War was in progress,​ which was called the war of Spartacus, Gellius​ was commander, while Cato took part in his campaign as a volunteer, for the sake of his brother; for his brother Caepio was a military tribune. 

Here he had not the opportunity to employ as much as he wished his zeal and discipline in virtue, because the war was not well conducted; but notwithstanding, amidst the great effeminacy and luxury of those who took part in that campaign, he displayed such good discipline, self-control, courage in all emergencies, and sagacity, that men thought him not one whit inferior to the elder Cato. 

Moreover, Gellius assigned to him prizes of valor and distinguished honors; but Cato would not take them nor allow them, declaring that he had done nothing worthy of honors. And so, in consequence of this, he was thought to be a strange creature. 

For instance, a law was passed forbidding candidates for office to be attended by nomenclators,​ and in his canvass for the military tribune­ship he was the only one who obeyed the law. 

He made it his business to salute and address without help from others those who met him on his rounds, but he did not avoid giving offense even to those who praised his course; for the more clearly they saw the rectitude of his practice, the more distressed were they at the difficulty of imitating it.