In the Name of Allah, the Gracious, the Merciful
Imam al-Nawawi records in his book Meadows of the Righteous:
باب في النصيحة
Chapter on sincere good will.
Source: Riyāḍ al-Ṣāliḥīn 1/81
Allah Almighty said:
إِنَّمَا الْمُؤْمِنُونَ إِخْوَةٌ فَأَصْلِحُوا بَيْنَ أَخَوَيْكُمْ وَاتَّقُوا اللَّهَ لَعَلَّكُمْ تُرْحَمُونَ
The believers are but one brotherhood, so make peace between your brothers. And be mindful of Allah so you may be shown mercy.
Surat al-Hujurat 49:10
And Allah said:
قَالَ يَا قَوْمِ لَيْسَ بِي ضَلَالَةٌ وَلَٰكِنِّي رَسُولٌ مِّن رَّبِّ الْعَالَمِينَ أُبَلِّغُكُمْ رِسَالَاتِ رَبِّي وَأَنصَحُ لَكُمْ وَأَعْلَمُ مِنَ اللَّهِ مَا لَا تَعْلَمُونَ
Noah replied, ‘O my people! I am not misguided! But I am a messenger from the Lord of all worlds, conveying to you my Lord’s messages and giving you sincere advice. And I know from Allah what you do not know.’
Surat al-A’raf 7:61-62
And Allah said:
قَالَ يَا قَوْمِ لَيْسَ بِي سَفَاهَةٌ وَلَٰكِنِّي رَسُولٌ مِّن رَّبِّ الْعَالَمِينَ أُبَلِّغُكُمْ رِسَالَاتِ رَبِّي وَأَنَا لَكُمْ نَاصِحٌ أَمِينٌ
Hud replied, ‘O my people! I am no fool! But I am a messenger from the Lord of all worlds, conveying to you my Lord’s messages. And I am your sincere advisor.’
Surat Al-A’raf 7:67-68
Tamim al-Dari reported: The Messenger of Allah, peace and blessings be upon him, said:
الدِّينُ النَّصِيحَةُ
Religion is sincerity.
It was said, “To whom?” He said:
لِلَّهِ وَلِكِتَابِهِ وَلِرَسُولِهِ وَلِأَئِمَّةِ الْمُسْلِمِينَ وَعَامَّتِهِمْ
To Allah, His Book, His Messenger, the leaders of the Muslims, and their common people.
Source: Sahih Muslim 55, Grade: Sahih
Jarir ibn Abdullah, may Allah be pleased with him, said:
بَايَعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَلَى السَّمْعِ وَالطَّاعَةِ وَأَنْ أَنْصَحَ لِكُلِّ مُسْلِمٍ
I swore allegiance to the Messenger of Allah, peace and blessings be upon him, pledging to listen and obey and to be sincere to every Muslim.
Source: Ṣaḥīḥ al-Bukhārī 57, Grade: Muttafaqun Alayhi
Anas ibn Malik reported: The Messenger of Allah, peace and blessings be upon him, said:
لَا يُؤْمِنُ أَحَدُكُمْ حَتَّى يُحِبَّ لِأَخِيهِ أَوْ قَالَ لِجَارِهِ مَا يُحِبُّ لِنَفْسِهِ
None of you has faith until he loves for his brother or his neighbor what he loves for himself.
Source: Ṣaḥīḥ al-Bukhārī 13, Grade: Muttafaqun Alayhi
In another narration, the Prophet said:
لَا يُؤْمِنُ أَحَدُكُمْ حَتَّى يُحِبَّ لِأَخِيهِ أَوْ قَالَ لِجَارِهِ مَا يُحِبُّ لِنَفْسِهِ
None of you will have faith until he loves for his brother or his neighbor what he loves for himself.
Source: Ṣaḥīḥ Muslim 45, Grade: Sahih
And in another narration, the Prophet said:
لَا يَبْلُغُ عَبْدٌ حَقِيقَةَ الْإِيمَانِ حَتَّى يُحِبَّ لِلنَّاسِ مَا يُحِبُّ لِنَفْسِهِ مِنَ الْخَيْرِ
The servant does not attain the reality of faith until he loves for people what he loves for himself of goodness.
Source: Ṣaḥīḥ Ibn Ḥibbān 235, Grade: Sahih
Success comes from Allah, and Allah knows best.