The second of the Jewish tribes in Medina were becoming alarmed by Mohammed's growing power and aggression. They began to hatch a plot against Mohammed. Unfortunately for them, Mohammed always had excellent intelligence. He heard of this and laid siege to their fort.
These Jews were farmers who grew very fine date palms. Mohammed burnt down many of these palm trees which incensed the Jews. They called out, “You have prohibited wanton destruction and blamed those who do that. Now you do what you forbid.”
The Jews were helpless however and cut a deal with Mohammed. They were allowed to leave with whatever they could carry, except for their armour and weapons. They even tore down their houses to take the wooden beams. These were valuable in Arabia where no trees grow. Since there was no fighting, Mohammed took 100% of the spoils. He spent this on his family and buying weapons for Jihad.
To answer his critics, The Koran brought down some new revelations. It was Allah who had wreaked vengeance which was the fault of the Jews.
From The Koran:
59:2 It was He who caused the People of the Book [the Jews] to leave their homes and go into the first exile. They did not think they would leave, and they thought that their fortresses could protect them from Allah. But Allah’s wrath reached them from where they did not expect it and cast terror into their hearts, so that they destroyed their homes with their own hands, as well as by the hands of the believers. Take warning from this example, you who have the eyes to see it!
B4,52,153 Because the property of the Jews that Allah had given to Mohammed had not been won by the Muslims through the use of their horses and camels, it belonged exclusively to Mohammed. He used it to give his family their yearly allowance and he spent the rest on weapons and horses for Jihad.
And The Sira:
I654 The Jews were very fortunate that Allah let them go with a few worldly processions. They got out alive and Allah did not slay them, but they would burn in Hell since they resisted Mohammed
Since the Kaffirs were the enemies of Allah, anything that Mohammed did to them was always justified. His doctrine of Jihad was taking shape as total warfare against the Kaffirs. He would accept no limitations on his ability to wage war against them. Allah would always provide justification for whatever rules he broke. Mohammed had now been in Medina for around three years.