2 Samuel 20:8

“When they [were] at the great stone which [is] in Gibeon, etc.] Which, according to Josephus f336, was forty furlongs, or five miles from Jerusalem: what this great stone was, whether an obelisk, or what, is not certain; one of the greatest stones we read of was that which Semiramis cut out of the mountains of Armenia, which was an hundred thirty feet long, and twenty five broad and thick f337. This place was appointed for the rendezvous of David’s forces, and hither Amasa came with what he had assembled together, and joined them, and took the command of them: for it follows, Amasa went before them; as the general of them: and Joab’s garment that he had put on was girded unto him; who went…”

“Amasa went before them--Having collected some forces, he by a rapid march overtook the expedition at Gibeon, and assumed the place of commander; in which capacity, he was saluted, among others, by Joab. Joab's garment, that he had put on was girded unto him--in the fashion of travellers and soldiers. a sword . . . and as he went forth it fell out--that is, out of the scabbard. According to JOSEPHUS, he let it drop on purpose as he was accosting Amasa, that stooping, as it were accidentally, to pick it up, he might salute the new general with the naked sword in his hand, without exciting any suspicion of his design. He went forth--in a ceremonious manner to meet Amasa, now commander-in-chief,…”

“Amasa went before them - Rather, “advanced to meet them.” Amasa was no doubt returning to Jerusalem, according to his orders 2 Samuel 20:4, and was probably much surprised to meet the army in march. Joab’s resolution was quickly taken. And Joab’s garment ... - Render, “And Joab was girded with his military garment, as his clothing, and upon it” - i. e., the military garment - (or “him”), “the girdle of a sword fastened on his loins in its sheath, and as he went forth” (to meet Amasa) “it fell” out of the sheath. What appears to have happened is that, by accident or design, Joab’s sword fell out of the scabbard on the ground as he was going to meet Amasa, and that he picked it up with his…”

“Amasa went - Having gathered some forces, and given due orders for the rest to follow him, he returned to Jerusalem, and by the king's command went after those mentioned Sa2 20:7, and being come up to them at the place where they waited for him, he put himself in the head of Joab's men, and the Cherethites and the Pelethites, and such as he had brought along with him, and marched before them as their general. Girded - After the manner of travellers and soldiers. Went forth - To meet and salute Amasa, who was coming towards him to do him honour. It fell - Things having (it is likely) been so contrived by Joab, that upon the least motion of his body, his sword should drop out, and he might…”

“in Gibeon: Sa2 2:13, Sa2 3:30 Amasa: Sa2 20:4, Sa2 20:5 2 Kings (2 Samuel) 20:9”