Flavius Josephus, Antiquities of the Jews
William Whiston, A.M., Ed.

[283] So Joab resolved to make no delay, but taking with him his brother, and those six hundred men, and giving orders that the rest of the army which was at Jerusalem should follow him, he marched with great speed against Sheba; and when he was come to Gibeon, which is a village forty furlongs distant from Jerusalem, Amasa brought a great army with him, and met Joab. Now Joab was girded with a sword, and his breastplate on; and when Amasa came near him to salute him, he took particular care that his sword should fall out, as it were, of its own accord: so he took it up from the ground, and while he approached Amasa, who was then near him, as though he would kiss him, he took hold of Amasa's beard with his other hand, and he smote him in his belly when he did not foresee it, and slew him. This impious and altogether profane action Joab did to a good young man, and his kinsman, and one that had done him no injury, and this out of jealousy that he would obtain the chief command of the army, and be in equal dignity with himself about the king; and for the same cause it was that he killed Abner. But as to that former wicked action, the death of his brother Asahel, which he seemed to revenge, afforded him a decent pretense, and made that crime a pardonable one; but in this murder of Amasa there was no such covering for it. Now when Joab had killed this general, he pursued after Sheba, having left a man with the dead body, who was ordered to proclaim aloud to the army, that Amasa was justly slain, and deservedly punished. "But," said he, "if you be for the king, follow Joab his general, and Abishai, Joab's brother:" but because the body lay on the road, and all the multitude came running to it, and, as is usual with the multitude, stood wondering a great while at it, he that guarded it removed it thence, and carried it to a certain place that was very remote from the road, and there laid it, and covered it with his garment. When this was done, all the people followed Joab. Now as he pursued Sheba through all the country of Israel, one told him that he was in a strong city, called Abelbeth-maachah. Hereupon Joab went thither, and set about it with his army, and cast up a bank round it, and ordered his soldiers to undermine the walls, and to overthrow them; and since the people in the city did not admit him, he was greatly displeased at them.