SRD:Gripsoul

Gripsoul
Gripsoul is a +6 keen longsword, but instead of dealing additional damage on a critical hit, the weapon imprisons the victim in a gem set in the pommel of the sword as per a binding spell heightened to 16th level (DC 30). The same is true of any blow that would otherwise kill a foe or knock him or her unconscious. Only one creature can be so held, but the wielder can release the bound soul at any time with a command word.

Caster Level: 27th; Prerequisites: Craft Magic Arms and Armor, Craft Epic Magic Arms and Armor, binding; Market Price: 1,856,500 gp; Cost to Create: 934,500 gp + 28,440 XP.