Pretty much every statement needs an authoritative resource. If it does not have one, or could not be personally confirmed by the editor, please use the Fact template:
Feel free to include a suitable explanation or the resource, that should contain the reference (for example, a book you have not read, but is quoted by Wikipedia). In general, you should refrain from quoting unsourced statements - a good exception would be historical statements of little controversy. Over time, most of the missing references should be corrected. Please use wisely.