And remember We took your covenant (to this effect): Shed no blood amongst you, nor turn out your own people from your homes: and this ye solemnly ratified, and to this ye can bear witness.
After this it is ye, the same people, who slay among yourselves, and banish a party of you from their homes; assist (Their enemies) against them, in guilt and rancour; and if they come to you as captives, ye ransom them, though it was not lawful for you to banish them. Then is it only a part of the Book that ye believe in, and do ye reject the rest? but what is the reward for those among you who behave like this but disgrace in this life?- and on the Day of Judgment they shall be consigned to the most grievous penalty. For Allah is not unmindful of what ye do.
What's the story behind those verses?
The Jewish tribes who lived on the outskirts of Medina had concluded an alliance with the Arab tribes of Aws and Khazraj. When the Arab tribes fought against one another each Jewish tribe fought on the side of its allies.when the war ended the captives were ransomed.So on the one hand the Jews fight each other although it is forbidden in the Jewish law but on the other hand they ransomed the captives cause it's a very important Jewish law.
Muhammad criticize the Jews that they not following the Jewish law completeness.
What's Muhammad viewpoint about the Jewish book?
And remember We took a covenant from the Children of Israel (to this effect): Worship none but Allah; treat with kindness your parents and kindred, and orphans and those in need; speak fair to the people; be steadfast in prayer; and practise regular charity. Then did ye turn back, except a few among you, and ye backslide (even now). And remember We took your covenant (to this effect): Shed no blood amongst you, nor turn out your own people from your homes: and this ye solemnly ratified, and to this ye can bear witness. (2:83-84)
In those verses Muhammad call the Jews to remember the Laws that were given to them in Mount Sinai.According those laws they should fight each other.
After this it is ye, the same people, who slay among yourselves, and banish a party of you from their homes; assist (Their enemies) against them, in guilt and rancour; and if they come to you as captives, ye ransom them, though it was not lawful for you to banish them. Then is it only a part of the Book that ye believe in, and do ye reject the rest? but what is the reward for those among you who behave like this but disgrace in this life?- and on the Day of Judgment they shall be consigned to the most grievous penalty. For Allah is not unmindful of what ye do. (2:85)
In this verse Muhammad criticize the Jews not following their laws.
His words are:
Then is it only a part of the Book that ye believe in, and do ye reject the rest?
So what can we learn from this?
Muhammad believed that the Jewish book a.k.a Torah was given to the Jews by Moses,So he can't understand how they not obey the law they shouldn't fight each other!
And it confirmed in 2:87 -We gave Moses the Book ... It's the same book Muhammad talked about on 2:85,the book the Jews should believe in...