Sunan Ibn Majah, Volume 3, Book 13, Hadith 2353 (DarusSalam) ⓘ
Kathir bin 'Abdullah bin 'Amr bin 'Awf narrated from his father that his grandfather said: “I heard the Messenger of Allah say: 'Reconciling between Muslims is permissible, except reconciliation that forbids something that is allowed, or allows something that is forbidden.'”
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا خَالِدُ بْنُ مَخْلَدٍ، حَدَّثَنَا كَثِيرُ بْنُ عَبْدِ اللَّهِ بْنِ عَمْرِو بْنِ عَوْفٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " الصُّلْحُ جَائِزٌ بَيْنَ الْمُسْلِمِينَ إِلاَّ صُلْحًا حَرَّمَ حَلاَلاً أَوْ أَحَلَّ حَرَامًا " .
also referenced under: Hadith 2353 (Reference) & Book 13, Hadith 46 (In-Book)