scabbard

他小心翼翼地将匕首插入刀鞘中。

He carefully slid the dagger into its ___scabbard.

他小心地将匕首插回刀鞘。

He carefully slid the dagger back into its ___scabbard.

武士小心地将剑插回剑鞘中。

The samurai carefully slid his sword back into the ___scabbard.