Genealogy software programs can help genealogists cite their source. Whole books, such as Evidence Explained, have been written providing guidelines for tracking where information was located. Remember that if nothing else, a citation should provide enough detail to get you back to the page in a book or piece of paper that provided you some information. If it doesn't, it's probably not adqeuate.
A relative said, "a newspaper in 1909 mentioned" a certain relative. At the very least, the name of the paper, date of publication, and whether it was the print, microfilm, or digital version would have been helpful. It's not always necessary to be 100% in the form of your citation, but it should allow someone else to re-find what you found--even if that "someone else" is you. After all, once in a while we need to review things for an additional viewing.