If you're looking for a meeting place or a good stop around ½ or halfway between Ashburn and Raleigh, you can try Petersburg, VA, which is about 2 hours south of Ashburn, or about 2½ hours northeast of Raleigh.
About ¼ or a fourth of the way, you can stop at New Post, VA. This is a little over 1 hour south of Ashburn.
About ⅓ or a third of the way, you can stop at Laurel, VA. This is about 1½ hours south of Ashburn.
About ⅔ or two thirds of the way, you can stop at Roanoke Rapids, NC. This is about 3 hours south of Ashburn, or about 1½ hours northeast of Raleigh.
About ¾ or three fourths of the way, you can stop at Delmar, NC. This is about 3½ hours south of Ashburn, or about 1 hour northeast of Raleigh.
If you drive straight through without stopping at all, the total distance is 298 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 4 hours, 29 minutes.