Narrated 'Amr bin 'Auf al-Muzani (RA):

Allah's Messenger (ﷺ) said: "Reconciliation is permissible between Muslims, except one which makes unlawful something which is lawful, or makes lawful something which is unlawful; and Muslims must abide by their conditions (which they have made), except for a condition which makes unlawful something which is lawful, or makes lawful something which is unlawful." [at-Tirmidhi reported it and graded it Sahih (authentic)]. However, the Hadith scholars criticized him (for grading this Hadith as Sahih) because the narration of Kathir bin 'Abdullah bin 'Amr bin 'Auf is weak. It is as though at-Tirmidhi considered it (reliable) due to its many chains of narration. Ibn Hibban declared the aforesaid Hadith to be Sahih (authentic) from the narration of Abu Hurairah (RA).

عَنْ عَمْرِو بْنِ عَوْفٍ اَلْمُزَنِيِّ ‏- رضى الله عنه ‏- أَنَّ رَسُولَ اَللَّهِ ‏- صلى الله عليه وسلم ‏-قَالَ: { اَلصُّلْحُ جَائِزٌ بَيْنَ اَلْمُسْلِمِينَ, إِلَّا صُلْحاً حَرَّمَ حَلَالاً وَ [1]‏ أَحَلَّ حَرَاماً، وَالْمُسْلِمُونَ عَلَى شُرُوطِهِمْ, إِلَّا شَرْطاً حَرَّمَ حَلَالاً وَ [2]‏ أَحَلَّ حَرَاماً } رَوَاهُ اَلتِّرْمِذِيُّ وَصَحَّحَهُ [3]‏ .‏ وَأَنْكَرُوا عَلَيْهِ; [4]‏ .‏ لِأَنَّ رَاوِيَهُ كَثِيرَ بْنَ عَبْدِ اَللَّهِ بْنِ عَمْرِوِ بْنِ عَوْفٍ ضَعِيفٌ [5]‏ .‏ وَكَأَنَّهُ اِعْتَبَرَهُ بِكَثْرَةِ طُرُقِهِ [6]‏ .‏ وَقَدْ صَحَّحَهُ اِبْنُ حِبَّانَ مِنْ حَدِيثِ أَبِي هُرَيْرَةَ [7]‏ .‏