For this reason, both parties accepted the idea of a temporary armistice; and the Muslim delegate insisted that it should expire by the end of the war with the Tatars. It is not acceptable, under Sharee‘ah, that Muslims make permanent peace with a usurper of Islamic territory, and it is not part of Sharee‘ah that Muslims should recognize a Crusader state or any such like over the Islamic land, no matter how old its occupation and settlement might be.
Although the Crusaders, at that time, had been living in Acre for 166 years, i.e. many generations were born, lived and died there, Qutuz, May Allaah have mercy upon him, never recognized the right of those usurpers in the Muslim Palestinian territory.

However, since Qutuz, May Allaah have mercy upon him, knew well that those Crusaders would never observe, concerning a believer, any pact of kinship or covenant of protection, he took his precautions by way of exhortation and intimidation. The Muslim delegate warned them severely that in case the treaty was broken, the Muslims would leave the Tatars and turn against the Crusaders, and would not cease until Acre would be liberated. A treaty established on the basis of power differs from a treaty established on the basis of weakness. The powerful always dictates his conditions, whereas the weak always submits to the conditions of the other. For this reason, if the Muslims concluded a treaty with other people, say, the Tatars, the Crusaders, the Jews, they should possess the means of punishing the other party in the event of violating the treaty or any article of it, otherwise, the treaty would be meaningless, for the other party would violate it once it finds an opportunity to do so.

{Is it not [true] that every time they took a covenant a party of them threw it away? But, [in fact], most of them do not believe.} [Quran 2:100]
As far as exhortation is concerned, Qutuz, May Allaah have mercy upon him, promised to sell them, in the event of victory, the Mongolian horses for a low price. That was indeed a great enticement due to the dire need of the people, emirs and army for horses, and the horses of the Tatars were famous for their strength.
Qutuz, May Allaah have mercy upon him, also agreed with the Crusaders of Acre that they should contribute to supplying the Muslim army with food and sustenance during their presence in Palestine; and the Crusaders approved.
Thus, the way to face the Tatars became safe. Qutuz, May Allaah have mercy upon him, and then started to put the final touches to his army in preparation for the meeting.

https://en.islamstory.com/index.php/en/artical/20795/temporary-armistice