Al-Mundhiri records in his book al-Targhib wal-Tarhib:

الترغيب في العفو عن القاتل والجاني والظالم والترهيب من إظهار الشماتة بالمسلم

Encouragement to pardon the murderer, offender, and wrongdoer, and discouragement of gloating by a Muslim.

Source: al-Targhīb wal-Tarhīb 3/208

‘Ubadah ibn al-Samit reported: The Messenger of Allah, peace and blessings be upon him, said:

ما مِنْ رَجُلٍ يُجْرَحُ فِي جَسَدِهِ جِرَاحَةً فَيَتَصَدَّقُ بِهَا إِلَّا كَفَّرَ اللهُ عَنْهُ مِثْلَ مَا تَصَدَّقَ بِهِ

No man suffers an injury to his body, and forgives it as charity, but that his sins will be expiated by the measure of his charity.

Source: Musnad Aḥmad 22701, Grade: Sahih li ghayrihi

Al-Muharrir reported: The Prophet, peace and blessings be upon him, said:

مَنْ أُصِيبَ بِشَيْءٍ فِي جَسَدِهِ فَتَرَكَهُ لِلَّهِ كَانَ كَفَّارَةً لَهُ

Whoever suffers injury to his body by someone in any way and he leaves it for the sake of Allah, it will be an expiation for him.

Source: Musnad Aḥmad 23494, Grade: Sahih li ghayrihi

Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said:

مَا نَقَصَتْ صَدَقَةٌ مِنْ مَالٍ وَمَا زَادَ اللَّهُ عَبْدًا بِعَفْوٍ إِلاَّ عِزًّا وَمَا تَوَاضَعَ أَحَدٌ لِلَّهِ إِلاَّ رَفَعَهُ اللَّهُ

Charity does not decrease wealth, no one forgives another but that Allah increases his honor, and no one humbles himself for the sake of Allah but that Allah raises his status.

Source: Ṣaḥīḥ Muslim 2588, Grade: Sahih

Abdur Rahman ibn Awf reported: The Messenger of Allah, peace and blessings be upon him, said:

ثَلاثٌ وَالَّذِي نَفْسُ مُحَمَّدٍ بِيَدِهِ إِنْ كُنْتُ لَحَالِفًا عَلَيْهِنَّ لَا يَنْقُصُ مَالٌ مِنْ صَدَقَةٍ فَتَصَدَّقُوا وَلا يَعْفُو عَبْدٌ عَنْ مَظْلَمَةٍ يَبْتَغِي بِهَا وَجْهَ اللهِ إِلَّا رَفَعَهُ اللهُ بِهَا عِزًّا وَلا يَفْتَحُ عَبْدٌ بَابَ مَسْأَلَةٍ إِلا فَتَحَ اللهُ عَلَيْهِ بَابَ فَقْرٍ

There are three, by the One in whose hand is the soul of Muhammad, I would swear an oath over if I were to do so: the wealth from charity is not reduced by giving charity, a servant does not forgive a wrong, seeking by it the countenance of Allah, but that Allah will raise his honor, and a servant does not open the door of begging but that Allah will open the door of poverty for him.

Source: Musnad Aḥmad 1674, Grade: Sahih li ghayrihi

Abu Kabshah reported: The Messenger of Allah, peace and blessings be upon him, said:

ثَلَاثَةٌ أُقْسِمُ عَلَيْهِنَّ وَأُحَدِّثُكُمْ حَدِيثًا فَاحْفَظُوهُ مَا نَقَصَ مَالُ عَبْدٍ مِنْ صَدَقَةٍ وَلَا ظُلِمَ عَبْدٌ مَظْلَمَةً فَصَبَرَ عَلَيْهَا إِلَّا زَادَهُ اللَّهُ عِزًّا وَلَا فَتَحَ عَبْدٌ بَابَ مَسْأَلَةٍ إِلَّا فَتَحَ اللَّهُ عَلَيْهِ بَابَ فَقْرٍ

I swear an oath by Allah on three qualities and I will you about them, so memorize them: the wealth of a servant is not decreased by charity, a servant is not wronged by oppression and he endures it patiently but that Allah increases him in honor, and no servant opens the door of begging but that Allah opens for him the door of poverty.

Source: Sunan al-Tirmidhī 2325, Grade: Sahih

Abdullah ibn Amr reported: The Prophet, peace and blessings be upon him, said:

ارْحَمُوا تُرْحَمُوا وَاغْفِرُوا يَغْفِرْ اللَّهُ لَكُمْ

Be merciful to others and you will receive mercy. Forgive others and Allah will forgive you.

Source: Musnad Aḥmad 6541, Grade: Sahih

Jarir ibn Abdullah reported: The Messenger of Allah, peace and blessings be upon him, said:

لَا يَرْحَمُ اللَّهُ مَنْ لَا يَرْحَمُ النَّاسَ

Allah will not be merciful to those who are not merciful to people.

Source: Ṣaḥīḥ al-Bukhārī 7376, Grade: Muttafaqun Alayhi

Ali reported: When the weapon of the Prophet, peace and blessings be upon him, had been assembled, I found on the handle or blade of his sword three sayings:

صِلْ مَنْ قَطَعَكَ وَقُلِ الْحَقَّ وَلَوْ عَلَى نَفْسِكَ وَأَحْسِنْ إِلَى مَنْ أَسَاءَ إِلَيْكَ

Maintain relations with those who cut you off, speak the truth even if it is against yourself, and be good to one who is evil to you.

Source: Mu’jam Ibn al-A’rābī 1507, Grade: Sahih

Aisha reported: Something of hers was stolen, so she began to supplicate against the thief. The Messenger of Allah, peace and blessings be upon him, said:

لَا تُسَبِّخِي عَنْهُ

Do not lighten his sin.

Source: Sunan Abī Dāwūd 4909, Grade: Sahih

Al-Subki commented on this tradition, writing:

فان السب والسرقة يوزنان يوم القيامة فإذا كان السب أقل من السرقة خفت جريمة السارق ورجع صاحب الحق بما بقي له وإذا كانت السرقة أقل من السب عاد السارق على الساب بما بقى له من الحق

For the curse and the theft will be weighed on the Day of Resurrection. If the curse is lesser than the theft, the crime of the thief is lessened and the rights are restored to the victim from what remains. If the theft is lesser than the curse, the thief will have his remaining rights restored from the one who cursed him.

Source: al-Manhal al-ʻAdhib al-Mawrūd 8/161