"This single blade did what we could not. It has brought us together. This blade has spilled the blood of Jaffa, of Tok'ra, and of Tau'ri. By the hand of our common enemy, it has made us brothers. Together we have ensured that it will never spill our blood again."
The A'tar Blade was a melee weapon used by Goa'uldAshrak assassins. They were a forged Naquadah blade that was capable of penetrating any form of armor.
The knife is used by an Ashrak who managed to get to the Tau'ri's Alpha Site, where he used it to kill Tok'ra, Jaffa, and Tau'ri. After the Ashrak was dead, Bra'tac hailed the knife as a symbol of the alliance between the Tok'ra, Jaffa and Tau'ri, because like the Goa'uld it had brought them together against a common enemy. (SG1: "Allegiance")