9 One would err, however, if he imagined that such a character as St. Francis de Sales possessed was a gift of nature, bestowed on him by the grace of God "with the blessing of meekness," as we so often read to have been the case of other blessed souls. On the contrary, Francis naturally was hot-tempered and easily aroused to anger. Since he had vowed to take as his model Jesus Who has said, "Learn of me, because I am meek, and humble of heart" ( Matt . xi, 29) so, by means of constant watchfulness over himself and of violence to his own will, he succeeded in learning how to curb and to control to such an extent the promptings of nature that he became a living likeness of the God of Peace and Meekness. This fact is proven amply by the testimony of the physicians who prepared his body for burial for when, as we read, they embalmed the body, they found his bile turned into stone which had been broken up into the smallest imaginable particles. They knew from this strange occurrence what terrible efforts it must have cost our Saint, over a period of fifty years, to conquer his naturally irritable temper.
Source: Rerum Omnium Perturbationem (Vatican.va)