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yā-ʾayyuhā lladhīna ʾāmanū ʾin tuṭīʿū farīqan mina lladhīna ʾūtū l-kitāba yaruddūkum baʿda ʾīmānikum kāfirīna
O you who have faith, if you obey a part of those who were given the Book, they will turn you back, after your faith, into faithless ones.
— Ali Quli Qarai
Surah 'Ali-Imran, Verse 100
100. "O' you who have Faith! If you hearken to a party from among of those who have been given the Book, they will turn you back, after your faith, into disbelievers."
In several books it is cited that one of the Jews by the name of Shash-ibn-Qays once passed by the gathering of Muslims consisting of members of two tribes called 'Aus and Khazraj and saw that they were very sincere with each other. He became worried about it and said to himself that formerly these two tribes were opposite to each other, but now, under the leadership and direction of Muhammad (S), they are living with each other peacefully. If this leadership continues, the existence of the Jews will be in danger.
He, systematically gathered a group to help him, and commissioned a young man to go inside them and to excite them by reminding them the memories of their fight in Biqath (the place where those two tribes fought against each other), so that the fire of a hard combat was going to be lit between them. The Prophet of Islam (S), with his soothing words, warned them and made them aware of that evil plot. Therefore, they put their swords down and kindly embraced each other while they were shedding tear and were regretful.
According to the commentators, in this incident, the above verse and the two former verses were revealed which caused the reproach and blame of the People of the Book as well as warning the Muslims.