In writing, citing an author means you quote, paraphrase or summarize the words of an external source and author and therefore should acknowledge this information is not yours through parenthetical documentation or citations. This according to the MLA manual which is the most common manual followed in academical writing can be included by writing the last name of the author and the page number in parentheses at the end of the citation or by mentioning during the text the last name of the author and including the page number in parentheses after the citation, this applies to all sources and authors that are cited once or multiple times except if the name of the author is not provided. According to this, in parenthetical documentation, you should include both the author's last name followed by a page number.
