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

الترغيب في زيارة الإخوان والصالحين وما جاء في إكرام الزائرين

Encouragement to visit the brethren and the righteous, and what has been related about honoring the visitors.

Source: al-Targhīb wal-Tarhīb 3/247

Abu Huraira reported: The Prophet, peace and blessings be upon him, said:

أَنَّ رَجُلًا زَارَ أَخًا لَهُ فِي قَرْيَةٍ أُخْرَى فَأَرْصَدَ اللَّهُ لَهُ عَلَى مَدْرَجَتِهِ مَلَكًا فَلَمَّا أَتَى عَلَيْهِ قَالَ أَيْنَ تُرِيدُ قَالَ أُرِيدُ أَخًا لِي فِي هَذِهِ الْقَرْيَةِ قَالَ هَلْ لَكَ عَلَيْهِ مِنْ نِعْمَةٍ تَرُبُّهَا قَالَ لَا غَيْرَ أَنِّي أَحْبَبْتُهُ فِي اللَّهِ عَزَّ وَجَلَّ قَالَ فَإِنِّي رَسُولُ اللَّهِ إِلَيْكَ بِأَنَّ اللَّهَ قَدْ أَحَبَّكَ كَمَا أَحْبَبْتَهُ فِيهِ

A man set out to visit his brother from another town, so Allah sent an angel to watch over his steps. When the angel came to him, he said: Where are you going? The man said: I am visiting a brother of mine in this town. The angel said: Do you have a favor over him to be repaid? He said: No, only that I love him for the sake of Allah Almighty. The angel said: I am a messenger from Allah to tell you that Allah loves you as you love him.

Source: Ṣaḥīḥ Muslim 2567, Grade: Sahih

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

مَنْ عَادَ مَرِيضًا لَمْ يَزَلْ فِي خُرْفَةِ الْجَنَّةِ حَتَّى يَرْجِعَ

Whoever visits a sick person will remain in an orchard of Paradise until he returns.

Source: Ṣaḥīḥ Muslim 2568, Grade: Sahih

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

إِنَّ اللَّهَ عَزَّ وَجَلَّ يَقُولُ يَوْمَ الْقِيَامَةِ يَا ابْنَ آدَمَ مَرِضْتُ فَلَمْ تَعُدْنِي قَالَ يَا رَبِّ كَيْفَ أَعُودُكَ وَأَنْتَ رَبُّ الْعَالَمِينَ قَالَ أَمَا عَلِمْتَ أَنَّ عَبْدِي فُلَانًا مَرِضَ فَلَمْ تَعُدْهُ أَمَا عَلِمْتَ أَنَّكَ لَوْ عُدْتَهُ لَوَجَدْتَنِي عِنْدَهُ

Allah Almighty will say on the Day of Resurrection: O son of Adam, I was sick but you did not visit Me. He will say: My Lord, how can I visit You when You are the Lord of the worlds? Allah will say: Did you not know that My servant was sick and you did not visit him, and had you visited him you would have found Me with him?

Source: Ṣaḥīḥ Muslim 2569, Grade: Sahih

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

مَنْ عَادَ مَرِيضًا أَوْ زَارَ أَخًا لَهُ فِي اللَّهِ نَادَاهُ مُنَادٍ أَنْ طِبْتَ وَطَابَ مَمْشَاكَ وَتَبَوَّأْتَ مِنْ الْجَنَّةِ مَنْزِلًا

Whoever visits a sick person or visits his brother for the sake of Allah, a heavenly caller will announce: May you be blessed, may your walking be blessed, and may you dwell in a residence of Paradise!

Source: Sunan al-Tirmidhī 2008, Grade: Sahih li ghayri

Anas reported: The Prophet, peace and blessings be upon him, said:

مَا مِنْ عَبْدٍ مُسْلِمٍ أَتَى أَخًا لَهُ يَزُورُهُ فِي اللَّهِ إلاَّ نَادَاهُ مُنَادٍ مِنَ السَّمَاءِ أَنْ طِبْتَ وَطَابَتْ لَكَ الْجَنَّةُ وَإِلَّا قَالَ اللَّهُ فِي مَلَكُوتِ عَرْشِهِ عَبْدِي زَارَ فِيَّ وَعَلَيَّ قِرَاهُ فَلَمْ يَرْضَ اللَّهُ لَهُ بِثَوَابٍ دُونَ الْجَنَّةِ

No Muslim servant visits his brother for the sake of Allah but that a caller from the heavens announces: You are purified and Paradise is purified for you! Otherwise, Allah says in the realms of His throne: My servant has visited Me and his guest for My sake, so I am not pleased for him to have any reward other than Paradise.

Source: Musnad al-Bazzār 6466, Grade: Hasan li ghayrihi

Anas ibn Malik reported: The Prophet, peace and blessings be upon him, said:

أَلَا أُخْبِرُكُمْ بِرِجَالِكُمْ فِي الْجَنَّةِ

Shall I not tell you about the best of your men?

We said, “Of course, O Messenger of Allah.” The Prophet said:

النَّبِيُّ فِي الْجَنَّةِ وَالصِّدِّيقُ فِي الْجَنَّةِ وَالشَّهِيدُ فِي الْجَنَّةِ وَالْمَوْلُودُ فِي الْجَنَّةِ وَالرَّجُلُ يَزُورُ أَخَاهُ فِي نَاحِيَةِ الْمِصْرِ لَا يَزُورُهُ إِلَّا لِلَّهِ فِي الْجَنَّةِ

The Prophet is in Paradise, the truthful are in Paradise, the martyrs are in Paradise, the child who dies is in Paradise, and a man who visits his brother in a faraway land, only visiting him for the sake of Allah, is in Paradise.

Source: al-Mu’jam al-Kabīr 1743, Grade: Hasan li ghayrihi

Mu’adh ibn Jabal reported: The Messenger of Allah, peace and blessings be upon him, said:

قَالَ اللَّهُ عَزَّ وَجَلَّ وَجَبَتْ مَحَبَّتِي لِلْمُتَحَابِّينَ فِيَّ وَالْمُتَجَالِسِينَ فِيَّ وَالْمُتَزَاوِرِينَ فِيَّ وَالْمُتَبَاذِلِينَ فِيَّ

Allah Almighty said: My love is assured for those who love each other for My sake, who sit together for My sake, who visit each other for My sake, and who spend on each other for My sake.

Source: Musnad Aḥmad 22030, Grade: Sahih

Jubayr ibn Mut’im reported: The Prophet, peace and blessings be upon him, said:

انْطَلِقُوا بِنَا إِلَى بَنِي وَاقِفٍ نَزُورُ الْبَصِيرَ رَجُلٌ كَانَ مَكْفُوفَ الْبَصَرِ

Come with us to the tribe of Waqif. We, who can see, will visit a man whose eyes cannot.

Source: Musnad al-Bazzār 3425, Grade: Sahih

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

زُرْ غِبًّا تَزْدَدْ حُبًّا

Visit the absent. It will increase your love.

Source: al-Mu’jam al-Kabīr 173, Grade: Sahih