Nahj al-Balāgha
Hadith 1642٦. وَقَالَ (عليه السلام): صَدْرُ الْعَاقِلِ صُنْدُوقُ سِرِّهِ وَالْبَشَاشَةُ حِبَالَةُ الْمَوَدَّةِ وَالِاحْتِمَالُ قَبْرُ الْعُيُوبِ.
6. Amīr al-mu’minīn, peace be upon him, said: The bosom of the wise is the safe of his secrets; cheerfulness is the bond of friendship; effective forbearance is the grave of short-comings.