Verse Two, in this song, has a Baha'i reference which will get the attention of any listener who knows their Baha'i catechism, so to speak.

"... the day when twenty thousand ... "

That number is much proclaimed and repeated as the initial number of Persian/Iranian nineteenth-century martyrs to the newly-appeared Baha'i "cause."

Recently one Western observer inquired, why has nobody put that number to the test? After all, the 'cause' acquired its first believers (and first martyrs in many cases) in 1844, and at no point before. It wasn't all that long ago; can't these things be documented somehow?

Of course, it would all be in Farsi/Persian language documentation.
That there were martyrs, and that their martyrdoms were often public spectacles, there is indeed record, and no doubt of it;
only the number is in question.
The Baha'is, and before them, the people known as Babis [long story], were never a really large number of people, especially in Ottoman Persia -- always a minority.
So the question more specifically is:
HOW many thousand?
Don't know if anyone would be satisfied with the answer, though, after all this time.