The information contained in a citation depends on the style guide you are following.
APA in-text citations, for example, include the author’s last name and the publication year, separated by a comma (e.g., Turing, 1947).
MLA citations include the author’s last name and the page number (e.g., Dahl 167).
Chicago citations include the author’s last name and the publication year, as well as the page number (e.g., Dahl 1961, 167).
Essentially, in-text citations must contain the necessary information for a reader to be able to identify the complete citation in your reference list.