Titus Livius (Livy), The History of Rome, Book 25
Frank Gardener Moore, Professor Emeritus in Columbia University, Ed.

18. While the consuls, on entering the Campanian region, were devastating it far and wide, being alarmed and dismayed by a sally of the Capuans and of Mago with his cavalry, they recalled their widely scattered soldiers to the standards, and being routed almost before their line was formed, lost over fifteen hundred men. [2] Upon this the great overconfidence of a people naturally proud was greatly increased, and they sought to provoke the Romans by many battles. But a single engagement incautiously and imprudently begun had made the consuls more careful to be on their guard. [3] One small occurrence, however, restored the courage of one army and lessened the boldness of the other. But in war nothing is so slight as not at times to bring about a great result. [4] Titus Quinctius Crispinus¹ had one Badius, a Campanian, as his guest-friend, linked to him by intimate hospitality. Friendship had grown because in an illness Badius had been generously and kindly nursed at the house of Crispinus at Rome before the rebellion of Campania. [5] This Badius at the time came up to the outposts stationed before the gate and bade them call [p. 413]Crispinus. When this was reported to Crispinus, he² went a little beyond the others, thinking a friendly and intimate conversation was wanted, since the memory of a personal tie lingered in spite of the rupture of public treaties. When they had come in sight of each other, “I challenge you to battle, Crispinus,” said Badius. [6] “Let us mount our horses and, with others kept at a distance, decide which is the better warrior.” In reply Crispinus said that neither he nor Badius lacked enemies on whom to show his courage. [7] For himself, even if he should meet the other in battle-line, he would avoid him, lest he stain his right hand with the blood of a guest-friend. And he turned and was walking away. [8] Then in truth the Campanian more fiercely reviled the effeminacy and cowardice of Crispinus and hurled reproaches which he himself deserved against an innocent man, calling him a guest-enemy and a man who pretended to spare one to whom he knew he was not equal. [9] If he thought that with the rupture of public treaties private ties had not also been broken, then, he said, Badius the Campanian, openly in the hearing of two armies, renounced the guest-friendship of Titus Quinctius Crispinus the Roman. [10] For himself, an enemy, nothing was hallowed by association, nothing by compact, with him, an enemy, since he had come to attack his native city and the Penates of the state and of the household. If he was a man, let him come on. [11] Crispinus, after long hesitation, was prevailed upon by his comrades not to allow the Campanian to revile him with impunity. [12] And so he delayed only long enough to consult the generals as to whether they permitted him to fight out of ranks against an enemy who challenged him. [p. 415]With their permission he took his arms and mounted³ his horse, and addressing Badius by name called him out to battle. [13] The Campanian made no delay; riding directly at each other they clashed. Crispinus with his spear pierced Badius' left shoulder above the shield; and after he fell wounded, leaped upon him from his horse, that, now dismounted, he might despatch the fallen. [14] Badius, not to be overpowered, left shield and horse and fled to his own men. [15] Crispinus, decked with spoils and displaying the horse and captured arms and his bloody spear, was conducted with much praise and congratulation on the part of the soldiers to the consuls, and there he was highly praised and rewarded with gifts.