(So judge between them by that which Allah hath revealed…) [5:49]. Said Ibn ‘Abbas: “A group of Jews which included Ka‘b ibn Asad, ‘Abd Allah ibn Suriya and Shas ibn Qays said to each other: ‘Let us go to Muhammad lest we seduce him from his religion’. When they went to him, they said: ‘O Muhammad, you know that we are the rabbis and nobles of the Jews, and if we were to follow you, the Jews will follow us without objection. We will believe in you and confirm your message in exchange for a favour: we have a dispute with some people and we want you to judge in our favour against them’. The Messenger of Allah, Allah bless him and give him peace, refused to do so, and Allah, exalted is He, revealed about them (… but beware of them lest they seduce thee from some part of that which Allah hath revealed unto thee…)”.
Asbab Al-Nuzul by Al-Wahidi , trans. Mokrane Guezzou