Unsurprisingly, St. Benedict beat me to the point of my previous post. Here is Chapter 72 of his Rule:
Of the Virtuous Zeal Which the Monks Ought to Have
As there is a harsh and evil zeal which separates from God and leads to hell, so there is a virtuous zeal which separates from vice and leads to God and life everlasting.
Let the monks, therefore, practice this zeal with most ardent love; namely, that in honor they forerun one another (cf Rom 12:10). Let them bear their infirmities, whether of body or mind, with the utmost patience; let them vie with one another in obedience. Let no one follow what he thinks useful to himself, but rather to another. Let them practice fraternal charity with a chaste love.
Let them fear God and love their Abbot with sincere and humble affection; let them prefer nothing whatever to Christ, and may He lead us all together to life everlasting.
The Latin for the word in bold is morum, which of course means "mulberry."
No, actually it means morals or character. St. Benedict tells his monks to bear each others' moral infirmities with the utmost patience, infirmitates suas patientissime tolerent.
I should probably point out that patience with infirmity is not indifference toward iniquity. Patience is essentially an internal matter; strictly speaking, I am not patient with someone else's infirmity directly, but with his infirmity as it exists in my mind and heart. As St. Augustine wrote:
The patience of man, which is right and laudable and worthy of the name of virtue, is understood to be that by which we tolerate evil things with an even mind, that we may not with a mind uneven desert good things, through which we may arrive at better.
To receive the moral infirmity of my Christian brother with an even mind, this is St. Benedict's advice; and St. Augustine's warning is that if I receive it with an uneven mind, I lose not only the good things impatience costs me directly, but the better things they would have brought me later.
Finally, St. Benedict's pairing of the physical and the moral -- "infirmitates suas sive corporum sive morum" -- suggests that impatience with moral infirmities makes no more sense, at least for the monk aspiring to perfection, than impatience with physical infirmities. We are, perhaps, more capable of overcoming moral infirmities than physical ones, but that doesn't make overcoming the moral ones the work of an instant. If someone I know to be habitually sullen acts sullen, is this a reasonable cause of impatience for me? How should I expect him to act?