Bukhari

Hadith Commentary: The Messenger of Allah (sallallahu alayhi wa sallam) never spoke ill of any believer throughout his life. Therefore, this noble statement was made out of perfect humility and compassion towards the people of faith. (sallallahu alayhi wa sallam)

Hadith Commentary:
(1)
The complete hadith is as follows: The Messenger of Allah sallallahu alayhi wa sallam said:
“O Allah! I make a covenant with You which You will not break. I am but a human being, so if I cause harm to any believer, revile him, curse him, or strike him, then make that for him a means of mercy, purification, and such nearness that will bring him close (to You) on the Day of Resurrection.”
(Sahih Muslim, al-Birr wa al-Silah, Hadith: 6619 (2601))

In another hadith, the background of this is also mentioned.
Aisha radi Allahu anha narrates that two men came to the Messenger of Allah sallallahu alayhi wa sallam.
It is not known what they said to him, but they made him angry, so he cursed them and spoke harshly to them.
When they left, I said:
“O Messenger of Allah! They will not benefit from anything.”
He said:
“How is that?” I replied:
“You cursed them and spoke harshly to them.”
He explained:
“Aisha! Do you not know what condition I have set with my Lord? I have said (to Allah):
O my Allah! I am only a human being, so for any Muslim whom I curse or speak harshly to, make that (cursing and harshness) for him a means of purification from sins and a means of reward.”
(Sahih Muslim, al-Birr wa al-Silah, Hadith: 6614 (2600))

(2)
This applies in the case when that person is not deserving of the curse, as clarified in another hadith. Thus, the Messenger of Allah sallallahu alayhi wa sallam said:
“If I supplicate against anyone from my ummah and he is not deserving of it, then O Allah! Make such supplication for him on the Day of Resurrection a means of purification, cleansing from sins, and such nearness by which You bring him close to Yourself.”
(Sahih Muslim, al-Birr wa al-Silah, Hadith: 6627 (2603))

Benefit:
This hadith proves that the Noble Prophet (sallallahu alayhi wa sallam) maintained a compassionate attitude towards people; he would not cause anyone harm, nor would he strike anyone, nor would he invoke curses upon anyone. It should be noted that implementing the prescribed punishments (hudud) and invoking curses against the disbelievers are exceptions to this. Some people, in the discussion of halalah, use the hadith of this chapter as a pretext to change the meaning of "curse" (la'nat) to "mercy," whereas this is a blatant mockery of the Qur'an and hadith, because any act upon which the word "curse" (la'nat) is used is considered a major sin (kabirah).