Hadith 31-104

وَبِهذَا الإِسنادِ قالَ: قالَ أَمِيرُ الْمُؤْمِنينَ عَلِىُّ بْنُ أَبِي طالِبٍ‏ عَلَيْهِ السَّلامُ: أَكمَلُكُم إِيماناً أحسَنُكُم خُلُقاً.

According to the same documentation, the Commander of the Faithful Ali ibn Abi Talib (a.s.) said, “Those of you who have the best temper are the ones with the most perfect faith.”