Ibn Rajab reported: It was said to Ibn al-Mubarak, may Allah have mercy on him, “Summarize good character for us in a single sentence.” Ibn al-Mubarak said, “Leave aside anger.”
Ibn Rajab said, “The same explanation was offered by Imam Ahmad and Ishaq ibn Rahawayh, that good character is to leave aside anger.”
Source: Jāmi’ al-‘Ulūm wal-Ḥikam 1/363
عن ابن رجب وَقِيلَ لِابْنِ الْمُبَارَكِ رحمه الله اجْمَعْ لَنَا حُسْنَ الْخُلُقِ فِي كَلِمَةٍ قَالَ تَرْكُ الْغَضَبِ
وقال ابن رجب وَكَذَا فَسَّرَ الْإِمَامُ أَحْمَدُ وَإِسْحَاقُ بْنُ رَاهَوَيْهِ حُسْنَ الْخُلُقِ بِتَرْكِ الْغَضَبِ
1/363 جامع العلوم والحكم