Midras Nahum 1:2: Kohelet Rabbah, Mekhilta DeRabbi Yishmael, Shemot Rabbah & Bereshit Rabbah

“Since the king's word has power, and who will say to him: What are you doing” (Ecclesiastes 8:4).
“Since the king's word has power.” Rabbi Bon said: It is written: “Do not test [the Lord]” (Deuteronomy 6:16), “and God tested [Abraham]” (Genesis 22:1), “Do not take vengeance and do not bear a grudge” (Leviticus 19:18), “the Lord is a zealous and vengeful God” (Nahum 1:2). [This is analogous] to a rabbi who would command his disciple, and say to him: ‘Do not divert judgment,’ but he [the rabbi] diverts judgment; ‘do not give preferential treatment,’ but he gives preferential treatment.²²A parallel midrash (Bereshit Rabba 55:3) adds the example: The rabbi tells him not to lend with interest, but he lends with interest. The disciple said to him: ‘Rabbi, for you it is permitted and for me it is prohibited?’ [The rabbi] said to him: ‘I am telling you only that you may not lend to an Israelite with interest, but lend to a gentile, as it is written: “You may take interest from a gentile” (Deuteronomy 23:21).’²³Thus, the rabbi informs his disciple that he did not fully understand any of the rabbi’s actions. So too, Israel said before the Holy One blessed be He: ‘Master of the universe, did You not write in Your Torah: “Do not take vengeance and do not bear a grudge” (Leviticus 19:18)? But You take vengeance and bear a grudge.’ He said to them: ‘I will not bear a grudge against Israel, as it is written: “He will not contend to eternity or forever bear a grudge” (Psalms 103:9); however, for the nations of the world: “The Lord is vengeful to His foes and bears a grudge against His enemies” (Nahum 1:2). I dictated to you in My Torah: “Do not take vengeance and do not bear a grudge against the members of your people” (Leviticus 19:18), but you may take vengeance against the nations of the world, as it is stated: “Avenge the children of Israel [on the Midianites]” (Numbers 31:2),’ to realize what is written: “Since the king's word has power, [and who will say to him: What are you doing].”

(Ibid.) "for I am the L–rd your G–d, a G–d of rancor": I rule over wrath and wrath does not rule over Me. As it is written (Nachum 1:2) "The L–rd is vengeful and the Master of wrath."

“These are the ordinances that you shall place before them” (Exodus 21:1).
“These are the ordinances [hamishpatim],” that is what is written: “The might of the King is that He loves justice [mishpat]” (Psalms 99:4). When is might ascribed to the Holy One blessed be He? When He executes judgment upon the idolaters. Thus you find regarding the wicked Nebuchadnezzar that because he boasted and said: “Is this not the great Babylon?” (Daniel 4:27), the Holy One blessed be He said to him: ‘Wicked one, putrid discharge, you boasted and said: Due to the greatness of my might and in honor of my splendor. Do you not know that everything is Mine; greatness is Mine, might is Mine, honor is Mine, and splendor is Mine?’ Likewise, David said: “Yours, Lord, is the greatness, and the might, and the splendor, and the triumph, and the glory” (I Chronicles 29:11). And it says: “The Lord my God, You have become exceedingly great” (Psalms 104:1). The Holy One blessed be He said to Nebuchadnezzar: ‘The limited royalty that has been given you is from Me.’ Likewise Daniel said to him: ‘“To whom the God of the heavens has given the kingdom, the power, the strength, and the glory” (Daniel 2:37), and you said: Due to the greatness of my might and in honor of my splendor?’ That is, “the might of the King is that He loves justice.” The might belongs to the King of kings, the Holy One blessed be He. He loves justice and He gave it to Israel who are His beloved.
That which is written: “You established equity [meisharim]” (Psalms 99:4); You established uprightness [yashrut] for Your beloved as, by means of the ordinances that You gave them, when they enter into disputes with one another they come to judgment and make peace.
Israel said before the Holy One blessed be He: ‘Master of the universe, until when will You refrain from executing justice upon the idolaters?’ He said to them: ‘Until their time will arrive to be harvested,’ as it is stated: “On that day, sing about it: a vineyard of wine” (Isaiah 27:2). Does a person pick his vineyard before it ripens? Rather, after it ripens, he picks it, places it into the wine press, stomps it, and sings, and [his fellows] answer after him. Thus the Holy One blessed be He said to Israel: ‘Wait for Me until the time of Edom will arrive, and I will stomp it, as it is stated: “I will cast my shoe at Edom” (Psalms 60:10). I will open for you and you will answer after Me.’ That is why it is stated: “Sing about it: a vineyard of wine.”
‘“I, the Lord, guard it; every moment I water it” (Isaiah 27:3). It is I who guards it in order to give it many [bitter] cups to drink, as it is stated: “Every moment I water it.” If I come to look at them, I will eliminate them from the world. However, “I have no fury” (Isaiah 27:4), like they become filled with fury against My children. Rather, what do I do to them? “I would trample and ignite them together” (Isaiah 27:4).’¹God is saying: Although Edom immediately acts with fury against My children, I do not do so against them. I wait for them, until their measure of sin is full, but then I will trample them and set them on fire.
Rabbi Levi said: The Holy One blessed be He said to the idolaters: ‘Israel is Mine,’ as it is stated: “For the children of Israel are servants to Me” (Leviticus 25:55). ‘Fury is Mine,’ as it is stated: “The Lord is vengeful and filled with fury” (Nahum 1:2). ‘You become filled with what is Mine,²Fury. against what is Mine,’ as it is stated: “If only I were given thorns and thistles in war” (Isaiah 27:4).³This is not cited as proof of the preceding statement but as a consequence; God says that He will, eventually, light the idolaters on fire like thorns and thistles.
The Rabbis say: The Holy One blessed be He said to them: ‘If I alter [meshaneh] My attribute of justice,⁴If I stop having patience with sinners. I will eliminate them with one lightning bolt [barak], as it is stated: “If I hone [shanoti] My flashing [berak] sword” (Deuteronomy 32:41). But what do I do? “My hand will grasp judgment”’ (Deuteronomy 32:41).⁵God says: I will continue My general course of judgment, which involves delaying judgment for sinners. Likewise it says: “He will grasp My stronghold [bema’uzi]” (Isaiah 27:5). Ma’uzi means nothing other than justice, as it is stated: “The might [oz] of the King is that He loves justice” (Psalms 99:4). The Holy One blessed be He said to Israel: ‘Just as I could violate justice for the idolaters, but I do not violate it, but rather grasp justice, so you shall not go outside the bounds of justice, as it is stated: “These are the ordinances [mishpatim].”