Jami` at-Tirmidhi 1580

Narrated Abu Al-Faid: "I heard Sulaim bin 'Amir saying: 'There was a treaty between Mu'awiyah and the people of Rome. He was making an expedition into their lands so that when the period of the treaty was expires he would attack them. So when a man upon an animal' - or - 'upon a horse said: "Allahu Akbar! Fulfillment not betrayal!" - and it turned out to be 'Amr bin 'Abasah - Mu'awiyah asked him about that. He said: "I heard the Messenger of Allah (ﷺ) said: 'Whoever has a treaty between himself and a people, then let him not violate the treaty nor try to change it until its time has passed, or , in retribution for a similar offense.'" He said: "So Mu'awiyah returned with the people." [Abu 'Eisa said:] This Hadith is Hasan Sahih