وَالَّذِينَ يَرْمُونَ أَزْوَاجَهُمْ وَلَمْ يَكُنْ لَهُمْ شُهَدَاءُ إِلَّا أَنْفُسُهُمْ فَشَهَادَةُ أَحَدِهِمْ أَرْبَعُ شَهَادَاتٍ بِاللَّهِ إِنَّهُ لَمِنَ الصَّادِقِينَ ﴿۶﴾ وَالْخَامِسَةُ أَنَّ لَعْنَتَ اللَّهِ عَلَيْهِ إِنْ كَانَ مِنَ الْكَاذِبِينَ ﴿۷﴾ وَيَدْرَأُ عَنْهَا الْعَذَابَ أَنْ تَشْهَدَ أَرْبَعَ شَهَادَاتٍ بِاللَّهِ إِنَّهُ لَمِنَ الْكَاذِبِينَ ﴿۸﴾ وَالْخَامِسَةَ أَنَّ غَضَبَ اللَّهِ عَلَيْهَا إِنْ كَانَ مِنَ الصَّادِقِينَ ﴿۹﴾

﴾6﴿ Wallazeena yarmoona azwaajahum wa lam yakul lahum shuhadaaa'u illaaa anfusuhum fashahaadatu ahadihim arba'u shahaadaatim billaahi innahoo laminas saadiqeen
﴾7﴿ Wallazeena yarmoona azwaajahum wa lam yakul lahum shuhadaaa'u illaaa anfusuhum fashahaadatu ahadihim arba'u shahaadaatim billaahi innahoo laminas saadiqeen
﴾8﴿ Wa yadra'u anhal 'azaaba an tashhada arba'a shahaa daatim billaahi innahoo laminal kaazibeen
﴾9﴿ Wal khaamisata anna ghadabal laahi 'alaihaaa in kaana minas saadiqeen

﴾6﴿ And those who accuse their wives (of adultery) and have no witnesses except themselves, then the testimony of one of them (the husband) shall be four testimonies [sworn] by Allah that indeed, he is truthful
﴾7﴿ And the fifth testimony is that the curse of Allah be upon him if he is among the liars
﴾8﴿ And it will avert the punishment from the woman if she testifies with four testimonies [sworn] by Allah that indeed, he (her husband) is among the liars
﴾9﴿ And the fifth [testimony] is that the wrath of Allah be upon her if her husband is among the truthful

[6,7,8,9] In these verses, the fourth ruling is mentioned to prevent the accusation of indecency between husband and wife through the procedure of li‘ān (mutual cursing). It is referred to as “four testimonies” because it is expressed with the phrase "I bear witness by Allah," which in meaning is like an oath.
In the fifth instance, the phrase "I bear witness" is not used. Rather, from the husband's side, it is a supplication of curse upon himself if he is lying, and from the wife's side, it is a supplication of wrath upon herself if the husband's claim turns out to be true.
Point (1): On the husband’s side, "curse" is mentioned, and on the wife's side, "wrath" is mentioned. One reason is that women often use curses casually and without concern, as mentioned in the hadith: “They frequently curse” (تَكْثُرْنَ اللَّعْن). For this reason, the word "wrath" is used for them. Men, on the other hand, avoid using the word "curse" frequently, so it is used for them here.
A second reason is that "wrath" is more intense than "curse," because curse implies deprivation from blessings, while wrath implies both deprivation and the descent of punishment and anger. So, when the husband's claim is proven true, the punishment for adultery applies to the wife, even though there is scholarly disagreement. And when the husband's claim is proven false, the punishment of lying applies to him, which is greater than the punishment for qadhf (false accusation).
A third reason is that the husband is more likely to be truthful in such situations, while a woman—even if she has committed adultery—may still lie. So, one who denies the truth knowingly is deserving of wrath, and thus wrath is mentioned regarding the wife.
Point (2): Since men are generally more calm and deliberate in speech, "(وَالْخَامِسَةُ)" is mentioned in a separate, independent form for the husband—linked grammatically to the previous phrases. But women often speak with haste, so "(وَالْخَامِسَةَ)" is mentioned in a connected form with the previous statement—grammatically a continuation of the prior sentence: أن تشهد الشهادة الخامسة... And Allah knows best.
Other rulings related to li‘ān are discussed in detail in hadiths and in Islamic jurisprudence.