It was narrated that 'Abdullah bin 'Amr bin 'As said:
"I heard the Messenger of Allah (ﷺ) say: 'The affairs of the Children of Israel remained fair until Muwalladun emerged among them - the children of female slaves from other nations. They spoke of their own opinions (in religious matters) and so they went astray and led others astray.'" (IT)
English reference (IT): Vol. 1, Book 1, Hadith 56 (IT)
Arabic reference (IT): Book 1, Hadith 58 (IT)