"By their friends shall ye know them"Since I haven't been able to find a reliable origin in nearly ten minutes of Google searching, I leave it to you, dear reader, to help me out. Upon discovering no immediately obvious origin, I was inclined to believe that this phrase was just a modification of a phrase from Mark, "By their fruits shall ye know them," that has been handed down for some time. But perhaps you'll discover something different. In fact, I hope you will. After all, I'd hate to see a phrase so poignant as this relegated to what I should think is a large pile of mis-translated sentences that simply stuck around.
If you find any of those, I'd enjoy mention of them, as well.