Type a parenthesis after the material you intend to cite and list the author's last name. If the work is by two authors, list both last names separated by an ampersand "&" each time you cite the work. If the work is by three to five authors, list all the authors the first time you cite the source. Use only the first author's last name followed by "et al." in subsequent citations. If the work is by six or more authors, use only the first author's name followed by "et al." each time you cite the work. Reference the APA manual for guidelines on how to cite sources outside of these examples.
Type a comma after the author's last name and type the abbreviation "n.d." for no date. Type a closing parenthesis and a period. A proper in-text citation where the author is known, but the date is unknown looks like this: (Abbott, n.d.).
Include specific page numbers in the in-text citation if you are quoting the author word for word. A proper in-text citation for a direct quotation when the date is unknown looks like this: (Abbott, n.d., pp. 111-112).