Books can be attributed to "Unknown" when the author or editor (as applicable) is not known and cannot be discovered. If at all possible, list at least one actual author or editor for a book instead of using "Unknown".
Books whose authorship is purposefully withheld should be attributed instead to Anonymous.
“the man who has good will for all, who is friendly and has compassion; who has no thoughts of ‘I’ or ‘mine’, whose peace is the same in pleasures and sorrows, and who is forgiving;”