Tarikh alkhulafa lilsuyudi
"It was narrated from zayd bin aslam who narrated from 'umar may God be pleased with them both that the prophet said" I saw a bunch of black goats that were joined by a bunch of white goats", they said what is your interpretation oh prophet of God, he said "the persians shall share with you your religion and lineage they said"the persians, oh prophet of God?" He said" if faith hung from a distant star, persians would still reach it, and would be the luckiest of them all"
"And it was narrated from 'umar bin sharjil that the prophet sallahu 'alayhi wa sallim said" I had a dream I was herding blacksheep, then I herded white sheep after them and until the black could no longer be seen", abu Bakr said" oh prophet of God, the black sheep are the arabs, they will become muslim and multiply, as for the white sheep they are the non-arabs, they will enter islam and so much so that the arabs wont be noticed from their sheer numbers,"the prophet salla lahu 'alayhi wa sallim said"an angel interpreted it just like that",
the prophet prophesized truthfully, the non-arabs entered the arabian peninsula in hoards during and after the islamic conquest, then did they mix among the arabs an excessive mixing, so much so that the arabs could not be seen any more because of their sheer numbers"
(Imam alsuyuti wrote this commentary in the 16th century around, although the hadith itself can be found in much older books like muhadarat aludba by rhagib alisfahani)