Preferably from a backup. If you don't have a backup, at least one company, Compunix, claims to have a product that will recover deleted files.
More information is available at .
If a file is Deleted from the system, the filesytem blocks composing that file still exist, but are no longer allocated. As long as no new files are created or existing files extended within the same filesystem, the blocks will remain untouched. This will display the inode information for the directory. The field a0 contains the block number of the directory. The following steps assume only field a0 is used.