Banu Nadir (Arabic: ??? ?????) were one of the three main Jewish tribes living in the 7th century of Medina, now in Saudi Arabia.
In early Medina, in addition to Banu Nadir, there were two other major Jewish tribes: Banu Qurayza and Banu Qaynuqa. The dominating tribes were the two non-Jewish Arab tribes, Banu Aus and Banu Khazraj.
Banu Nadir settled outside the city of Yathrib, now Medina, because of the Roman persecutions of the Jews in Palestine. According to the Muslim historian al-Yaqubi, Banu Nadir were an Arab tribe ethnically, which had converted to Judaism and initially settled on the eponymous Mount Nadir. Some, however, believe them to be an ethnically Jewish tribe connected with the Khaybar Jews. [Please name specific person] Like other Medinese Jews, Banu Nadir bore Arabic names, but spoke a distinct dialect of Arabic. They earned their living through agriculture, money lending, and trade in weapons and jewels, maintaining commercial relations with Arab merchants of Mecca. Their fortresses were located half a day`s march to the south of Medina.  Banu Nadir were wealthy and were lived in some of the best lands in Medina. 
Before Muhammad: 610s
In the 610s, the chiefs of Banu Nadir were Ka`b ibn al-Ashraf, a gifted poet, and Huyayy ibn Akhtab. Those two tribes went to war against each other in the Battle of Bu`ath, and the three Jewish tribes split on different sides of the war. During the battle, Banu Nadir and Banu Qurayza fought with Banu Aus, while Banu Qaynuqa were allied with Banu Khazraj. The latter were defeated after a long and arduous battle. 
Arrival of Muhammad: 622
Muhammad was invited to Medina to broker a peace between the warring tribes, and in September 622, he arrived with a group of his followers, who were given shelter by members of the indigenous community known as the Ansar. Amongst his first actions was the construction of the first Mosque in Medina, as well as obtaining residence with Abu Ayyub al-Ansari. He then set about the establishment of a pact, known as the Constitution of Medina, between the Muslims, the Ansar, and the various Jewish tribes of Medina  to regulate the matters of governance of the city, as well as the extent and nature of inter-community relations. Conditions of the pact included boycotting Quraysh, abstinence from "extending any support to them", assistance of one another if attacked by a third party, as well as "defending Medina, in case of a foreign attack". It was later that certain tribes would be claimed to have violated this pact due to supporting enemy forces, such as Quraysh, against the Muslims.
Expulsion of the Banu Qaynuqa from Medina: 624
In March 624, Muslims led by Muhammad defeated the Meccans of the Banu Quraish tribe in the Battle of Badr. Muhammad had been in conflict with his own former tribe, Banu Quraish, since he left it to found Islam. His victory allowed him to return to Medina.
After a few years, a dispute broke out between the Muslims and Banu Qaynuqa. A Jewish man was alleged to have pinned the clothing of Muslim woman sitting in a jeweler`s shop in the Qaynuqa marketplace, so that she was stripped naked when she stood up. A Muslim man coming upon the resulting commotion killed the shopkeeper in retaliation. This escalated to a chain of revenge killings. Soon full-scale civil war broke out.
Muhammad approached Banu Qaynuqa (the allies of the Khazraj tribe), in light of these hostilities, gathering them in the market place and addressing them as follows:
"O assembly of Jews, beware that something from God befalls you similar to the curse that descended upon Quraysh, and enter into Islam, for you have known that I am a Prophet that has been sent, due to what you find in your Book and the covenant of God to you"
"O Muhammad, you seem to think that we are your people. Do not deceive yourself because you vanquished a contingent of Quraysh having no knowledge of war and got the better of them; for, by God, if we fight you, you will find that we are real men, and that you have not met the likes of us"  (declared by Ibn Hajar to be hasan).
It was this exchange which resulted in what is known as the siege of Banu Qaynuqa , which lasted for fourteen to fifteen days, after which the tribe surrendered unconditionally. Muhammad consented to Banu Qaynuqa being expelled when Abdallah ibn Ubayy, the chief of the Khazraj, pleaded before Muhammad on their behalf.
Banu Nadir remained non-pariticpants during the Banu Qaynuqa episode, viewing the conflict as another example of a typical tribal struggle.  The conflict led to a ruling that such future action by any of the other parties to the Constitution of Medina would constitute a voiding of their benefits under