How harmful is gasoline residue inside the crank case?

Me & a buddy put a Honda Shadow back together & had a hose crossed & caused it to run horribly. We fixed the issue, but we smelled gas in the oil so we changed it. There's still a smell of it on the dipstick. How harmful is it to the motor?

If a significant amount of raw gas was dumped into your crankcase, drain the oil and put in fresh.
Oil is the "lifeblood" of your engine, and a few quarts of new oil is a very economical preventative measure to potential serious engine compromise. Even in doubt, do it to be on the safe side.
Oil" breaks down" and thins with gasoline AND oil's ability to lubricate is compromised as well.
I do not agree with some of the other avatars to just go ahead and take a chance and run the engine. Too, if there's a significant amount of raw gas in the crank case, when you run it, (if the engine doesn't seize first), it will heat up and may at some point CATCH FIRE… No joke!
Better safe than sorry.

Yes gasoline is bad for your oil. Drop the oil pan to see how much gas in actually in there. Might need to flush your engine out with oil. There are many patches and spots where oil sits and doesn't really get changed out in a normal oil change. Might have gas in those spots

Gasoline will evaporate fairly quickly once the engine is up to operating temperature. The SMELL may remain for a while, but I doubt there's anything serious to worry about

It'll be fine after the oil change. Gas evaporates.