Kitāb al-Muʾmin
Hadith 3636 - وعن أبي عبد الله (ع) أنه قال نِعمَ الجُرعةُ الغيظ لمَن صَبرَ عَليها، فإنّ عظيمَ الأجر لمَعَ عظيمِ البلاءِ، وما أحبَّ اللهُ قوماً إلاّ ابتَلاهم.
36. It has been narrated that Abu 'Abd Allah (a.s) said: The best of 'gulps' is anger that is swallowed despite being unbearable; for the greatest reward comes with the greatest affliction. Allah never loved people but that He tried them (with afflictions).