I shaved my face clean about 40 days and have shaved multiply times since then. I just recently started to grow a beard for the last 20 days or so. Will this hair be clean if I haven't done anything in the past 50 days? Even then it was a single time use.

If it's really only one time, you're probably ok.

You are aware they could pick eyelash hair, or eyebrow hair... just as easily as buttcrack hair or any other hair.

Smoothy is correct. The testing facility usually gets to chose the site. The most frequent site is the scalp hair. If your head is shaved and you have 0.5 inches of beard growth, then it will likely be the site of harvest. You will be fine if it is from the beard.

Regardless of the site, if you have only used occasionally over 50 days ago, you will be clean on any hair test.

A hair test won't show one time use. All hair drug tests are meant to show consistent use over time. Yours was not consistent use. I wouldn't worry.

You should be fine.