Petrifying Dagger weapon, very rare

This ornamental dagger is made from stone and edged in gold. Embedded along its spine there are three polished obsidian beads. When you hit a creature with this weapon you can cast Flesh to Stone, spell save DC 17, on the target creature. If the creature is petrified by this effect one of the obsidian beads shatters. 

Once used, this property of the dagger can’t be used again until the next dawn. After all three beads are shattered this weapon becomes a nonmagical dagger.