Jami` at-Tirmidhi 1580
جامع الترمذي#1580Sahihحَدَّثَنَا مَحْمُودُ بْنُ غَيْلاَنَ، حَدَّثَنَا أَبُو دَاوُدَ، قَالَ أَنْبَأَنَا شُعْبَةُ، قَالَ أَخْبَرَنِي أَبُو الْفَيْضِ، قَالَ سَمِعْتُ سُلَيْمَ بْنَ عَامِرٍ، يَقُولُ كَانَ بَيْنَ مُعَاوِيَةَ وَبَيْنَ أَهْلِ الرُّومِ عَهْدٌ وَكَانَ يَسِيرُ فِي بِلاَدِهِمْ حَتَّى إِذَا انْقَضَى الْعَهْدُ أَغَارَ عَلَيْهِمْ فَإِذَا رَجُلٌ عَلَى دَابَّةٍ أَوْ عَلَى فَرَسٍ وَهُوَ يَقُولُ اللَّهُ أَكْبَرُ وَفَاءٌ لاَ غَدْرٌ . وَإِذَا هُوَ عَمْرُو بْنُ عَبَسَةَ فَسَأَلَهُ مُعَاوِيَةُ عَنْ ذَلِكَ فَقَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " مَنْ كَانَ بَيْنَهُ وَبَيْنَ قَوْمٍ عَهْدٌ فَلاَ يَحُلَّنَّ عَهْدًا وَلاَ يَشُدَّنَّهُ حَتَّى يَمْضِيَ أَمَدُهُ أَوْ يَنْبِذَ إِلَيْهِمْ عَلَى سَوَاءٍ " . قَالَ فَرَجَعَ مُعَاوِيَةُ بِالنَّاسِ . قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ .
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
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
In-book reference: 21:42