al-Mandhar bin Malik bin Qata' المنذر بن مالك بن قطعة - أبو نضرة العبدي · The Book of the Sunnah

"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.'"

"One day the Prophet (ﷺ) appeared among the people. A man came to him and said: 'O messenger of Allah, what is Iman (faith)?' He said: 'To believe in Allah, His angels, His books, His Messengers and the meeting with, and to believe in the Final Resurrection.' He said: 'O Messenger of Allah, what is Islam?' He said: 'To worship Allah (alone) and not to associate anything with Him; to establish the prescribed prayers, to pay the obligatory Zakat, and…