I heard that St. Francis de Sales struggled with a temper problem for many years, but he overcome it. What is the source of this biographical information?
Loiuse M. Stachoople-Kenny's biography, for example, seems to only mention his sweet temper, but nothing about how he fought to overcome his naturally choleric temperament:
Francis never lost his temper, was always patient and good-humoured, submitting with a smile to the constant rebukes of his old tutor, and treating him always with unfailing gentleness and kindness. As a matter of fact, M. Déage really worshipped the very ground his beloved pupil walked on, but like many people, ready to die for those they love, he tantalized and tormented with constant pinpricks, growls and grumbles, the man he loved most on earth; indeed, his affection and his temper would have made life unbearable to anyone less sweet-tempered and kind-hearted than the gentle Bishop of Geneva.