beside the point
Also, beside the mark or question. Irrelevant, off the subject. For example, Whether you had insurance is beside the point; the accident is your fault. These terms came into common use in the mid-1800s. Also see neither here nor there.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.