First, unless you are in a rural plains state or something 3 miles is a long clip. Maybe from a mountain top, sky scraper to sky scraper, or something. In my rural New England area I can only think of a few places where I have that long a line of sight.

That being said I have one of these: https://www.amazon.com/gp/product/B01MXIAKSP It all depends on what you want. 3 miles AND read a person's name tag? That's telescope country there, and without stabilization unlikely to be possible. To be able to tell 3 males are standing by the back door of that warehouse? I would think that was totally possible with the above unit, if you do your part. Heck I think I have a straight shot of road that long maybe I'll clock off 3 miles and see what I can see, pun intended.