Summer Sources: Anger
(לב) ט֤וֹב אֶ֣רֶךְ אַ֭פַּיִם מִגִּבּ֑וֹר וּמֹשֵׁ֥ל בְּ֝רוּח֗וֹ מִלֹּכֵ֥ד עִֽיר׃

(32) Better to be slow to anger than mighty, To have self-control than to conquer a city.

ר"ל אמר כל אדם שכועס אם חכם הוא חכמתו מסתלקת ממנו אם נביא הוא נבואתו מסתלקת ממנו אם חכם הוא חכמתו מסתלקת ממנו ממשה דכתיב (במדבר לא, יד) ויקצוף משה על פקודי החיל וגו' וכתיב (במדבר לא, כא) ויאמר אלעזר הכהן אל אנשי הצבא הבאים למלחמה זאת חוקת התורה אשר צוה ה' את משה וגו' מכלל דמשה איעלם מיניה
Similarly, Reish Lakish said: Any person who becomes angry, if he is a Torah scholar, his wisdom departs from him, and if he is a prophet, his prophecy departs from him. The Gemara explains: That if he is a Torah scholar his wisdom departs from him is learned from Moses, as it is written: “And Moses became angry with the officers of the host, the captains over thousands and the captains over hundreds, who came from the battle” (Numbers 31:14). And what was his punishment? As it is written afterward: “And Elazar the priest said to the men of war who went to the battle: This is the statute of the law, which the Lord commanded Moses” (Numbers 31:21), which proves by inference that this law had become hidden from Moses due to his anger.
אמר רבה בר רב הונא כל הכועס אפילו שכינה אינה חשובה כנגדו שנאמר רשע כגובה אפו בל ידרוש אין אלהים כל מזמותיו רבי ירמיה מדיפתי אמר משכח תלמודו ומוסיף טיפשות שנאמר כי כעס בחיק כסילים ינוח וכתיב וכסיל יפרוש אולת רב נחמן בר יצחק אמר בידוע שעוונותיו מרובין מזכיותיו שנאמר ובעל חימה רב פשע
Rabba bar Rav Huna said: Anyone who gets angry, at that moment even the Divine Presence is not important to him, as it is stated: “The wicked, in the height of his anger says: He will not require; all his thoughts are: There is no God” (Psalms 10:4). Rabbi Yirmeya of Difti said: Anyone who gets angry forgets his learning and increases foolishness, as it is stated: “For anger rests in the bosom of fools” (Ecclesiastes 7:9), and it is written: “But a fool unfolds folly” (Proverbs 13:16). Rav Naḥman bar Yitzḥak said: With regard to one who gets angry, it is acknowledged that his sins are more numerous than his merits, as it is stated: “And a wrathful man abounds in transgression” (Proverbs 29:22).
א"ר אילעאי בשלשה דברים אדם ניכר בכוסו ובכיסו ובכעסו ואמרי ליה אף בשחקו:
Rabbi Elai said: In three matters a person’s true character is ascertained; in his cup, i.e., his behavior when he drinks; in his pocket, i.e., his conduct in his financial dealings with other people; and in his anger. And some say: A person also reveals his real nature in his laughter.

(ג)... לְפִיכָךְ צִוּוּ לְהִתְרַחֵק מִן הַכַּעַס עַד שֶׁיַּנְהִיג עַצְמוֹ שֶׁלֹּא יַרְגִּישׁ אֲפִלּוּ לַדְּבָרִים הַמַּכְעִיסִים וְזוֹ הִיא הַדֶּרֶךְ הַטּוֹבָה. וְדֶרֶךְ הַצַּדִּיקִים הֵן עֲלוּבִין וְאֵינָן עוֹלְבִין שׁוֹמְעִים חֶרְפָּתָם וְאֵינָם מְשִׁיבִין עוֹשִׂין מֵאַהֲבָה וּשְׂמֵחִים בְּיִסּוּרִים. וַעֲלֵיהֶם הַכָּתוּב אוֹמֵר (שופטים ה לא) "וְאֹהֲבָיו כְּצֵאת הַשֶּׁמֶשׁ בִּגְבֻרָתוֹ":

(3)...The sages have therefore directed that a man should remove from anger, and train himself so as not to take notice even of things provoking; this being the good way. Now the way of the righteous is this: They may be derided, yet they do not deride others; they hear themselves reproached, yet do not reply; they do every thing out of love to God, and are cheerful in affliction; and with regard to them Scripture says: But let them that love Him be as the sun when he goeth forth in his might, (Judg. 5. 31).