Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
tabarani:21763 – Isḥāq b. Dāwud al-Ṣawwāf al-Tustarī > Abū al-Ashʿath Aḥmad b. al-Miqdām > Fuḍayl b. Sulaymān al-Numayrī > ʿAbd al-Raḥman b. Ḥumayd from his father > Um Kulthūm b. ʿUqbah

[Machine] She heard the Messenger of Allah ﷺ saying, "He is not a liar who reconciles between two people."  

الطبراني:٢١٧٦٣ – حَدَّثَنَا إِسْحَاقُ بْنُ دَاوُدَ الصَّوَّافُ التُّسْتَرِيُّ ثنا أَبُو الْأَشْعَثِ أَحْمَدُ بْنُ الْمِقْدَامِ ثنا فُضَيْلُ بْنُ سُلَيْمَانَ النُّمَيْرِيُّ حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ حُمَيْدٍ عَنْ أَبِيهِ عَنْ أُمِّ كُلْثُومٍ بِنْتِ عُقْبَةَ

أَنَّهَا سَمِعَتْ رَسُولَ اللهِ ﷺ يَقُولُ «لَيْسَ بِالْكَاذِبِ الَّذِي يُصْلِحُ الرَّجُلُ بَيْنَ اثْنَيْنِ»  

See similar narrations below:

Collected by Ibn Ḥibbān
ibnhibban:5733 – Abū Ḥātim > ʿUmar b. Muḥammad al-Hamdānī > ʿAbd al-Malik b. Shuʿayb b. al-Layth from my father from my father > Yaḥyá b. Ayyūb > Mālik b. Anas > Ibn Shihāb > Ḥumayd b. ʿAbd al-Raḥman b. ʿAwf > Ummih Um Kulthūm b. ʿUqbah

"One who brings peace between people is not a liar, he says something good, or reports something good." (Using translation from Tirmidhī 1938)   

ابن حبّان:٥٧٣٣ – حَدَّثَنَا أَبُو حَاتِمٍ ؓ قَالَ أَخْبَرَنَا عُمَرُ بْنُ مُحَمَّدٍ الْهَمْدَانِيُّ قَالَ حَدَّثَنَا عَبْدُ الْمَلِكِ بْنُ شُعَيْبِ بْنِ اللَّيْثِ قَالَ حَدَّثَنِي أَبِي عَنْ جَدِّي عَنْ يَحْيَى بْنِ أَيُّوبَ عَنْ مَالِكِ بْنِ أَنَسٍ عَنِ ابْنِ شِهَابٍ عَنْ حُمَيْدِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ عَوْفٍ عَنْ أُمِّهِ أُمِّ كُلْثُومَ بِنْتِ عُقْبَةَ

أَنَّهَا سَمِعَتْ رَسُولَ اللَّهِ ﷺ يَقُولُ «لَيْسَ الْكَذَّابُ الَّذِي يُصْلِحُ بَيْنَ النَّاسِ فَيُنْمِي خَيْرًا أَوْ يَقُولُ خَيْرًا»