The Banu Qaynuqa (also spelled Banu Kainuka, Banu Kaynuka, Banu Qainuqa, Arabic: ??? ???????) were one of the three main Jewish tribes living in the 7th century of Medina, now in Saudi Arabia.
In the 7th century, the Banu Qaynuqa were living in two fortresses in the south-western part of the city of Yathrib, now Medina, having settled there at an unknown date. Although the Banu Qaynuqa bore mostly Arabic names, they were both ethnically and religiously Jewish. They owned no land, earned their living through commerce and craftsmanship, including goldsmithery. The Banu Qaynuqa were allied with the local Arab tribe of Khazraj and supported them in their conflicts with the rival Arab tribe of Aws. 
Arrival of Muhammad
In September 622, Muhammad arrived at Medina 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 Quraish, against the Muslims.
Expulsion of the Banu Qaynuqa
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. Some sources say the reasons given by Muslim historians are backdated attempts to justify the attack on the Jewish tribe and the incidents, like the one of the Jewish goldsmith, have no more than anecdotal value, while some Islamic scholars consider it as part of the Divine punishment by believers after clarification of the truth in its ultimate form.
Muhammad divided the property of the Banu Qaynuqa, including their arms and tools, among his followers, taking for himself a fifth share of the spoils for the first time. Some members of the tribe chose to stay in Medina and embraced Islam, more in order to retain their belongings than out of conviction (dubious assertion—see talk page) . The only Banu Qaynuqa man who became a devout Muslim was Abdullah ibn Sailam. Although some Muslim sources claim that he converted immediately after Muhammad’s arrival to Medina, academic scholars give more credence to the other Muslim sources, which indicate that 8 years later, 630, as the year of ibn Salam’s conversion. 
Muhammad as a General
Rules of war in Islam
^ a b c Weinsinck, R.J. and Paret, R.. "Kaynuka, Banu". Encyclopaedia of Islam Online Edition. Ed. P.J. Bearman, Th.