There is no need to threaten - I feel that we have been able to disagree very amicably up till now and are working well to come to a resolution which meets wikipedia's policies and procedures. I'm not putting WP:OR into an article, nor am I doing any. (Okay, I suppose calling it an urban legend was my own term and is WP:OR, but I was doing that conversationally and would never dream of putting it in the article). I simply said that this fact, if included, had to have a WP:RS. I have presented about a dozen or so sources, none of which include this. You have found one source, which is far less reliable than any of the ones I have brought, which mentions it as something rarely done today. I'm simply asking that this fact be sourced properly and that that be reflected in the article - something which you seem to be open to as well. If we use the BBC source, then we should probably also mention that none of the three major rabbinic organizations include this rule. (Citing their rules which I included links to in my previous comment). To clarify I'm not suggesting we use use the phrase "urban legend" in the article at all - I'm just saying that we need a better source than the original one and that the scope of the source be reflected.
Frankly I understand your somewhat visceral reaction. This idea is so pervasive that it has almost become a reality in and of itself in that perception frequently affects reality. I was taught that it was true, and took it as fact until recently when I had a conversation with a rabbi who does conversions for the RCA and helped draft their policies. Only afterwards did I start digging and realized it had no source. It is impossible to prove a negative so I can't prove to you that it doesn't exist "somewhere". However I can insist that we use a WP:RS. If you can find a reliable Jewish source, either classical or contemporary, for this then by all means include it with that source, but so far none has been located.   
As a side note here's another article on Marc Angel's group's website which would probably count as a RS - it's not in the description there either.