Blade of the Sun and Moon

Liber Mysterium
The Netbook of Witches and Warlocks
By Timothy S. Brannan and The Netbook of Witches and Warlocks Team
Full netbook can be found on the followng website
Dom of D20 / D&D 3e Netbooks and Downloads.

During the daytime, this longsword functions as a +2 flaming burst weapon. During the night, it functions as an icy weapon, with the additional ability that whenever it strikes a critical hit, the victim must make a will save DC 15 or come under the effects of a Sleep spell.

Caster Level: 15th; Prerequisites: Craft Magical Arms and Armour, Astromancy, Sleep Market Price: 50,000 GP, cost to Create: 25,000 GP + 1000 XP