The Prophet ﷺ said, "There is no Muslim servant who goes to visit his brother for the sake of Allah except that a caller from heaven calls out to him, 'You have done well, and Paradise is yours.' And Allah declares from the dominion of His Throne, 'My servant has visited for My sake, and it is upon Me to host him,' and Allah is not pleased with any reward for him short of Paradise."
عن النبي ﷺ قال: ما من عبد مسلم أتى أخا له يزوره في الله، إلا ناداه مناد من السماء: أن طبت، وطابت لك الجنة، وإلا قال الله في ملكوت عرشه: عبدي زار في، وعلي قراه، فلم يرض الله له بثواب دون الجنة.
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Bazzar (6466), Abu Naeem in Hilya (3/107), and Abu Yaala (4140) - and by his route, Diya in Mukhtara (7/236) - all narrated it via Yusuf bin Yaqub Dubai Sadusi, who said, Maymun bin Ajlan told us, from Maymun bin Siyah, from Anas bin Malik, who mentioned it. Its chain is hasan because of Maymun bin Siyah, for his hadith is hasan so long as nothing contrary appears, and likewise Maymun bin Ajlan is hasan in his hadith. Abu Hatim said of him, "A shaykh," and Ibn Hibban mentioned him among the trustworthy narrators. Munziri said in Targhib (3914), "Bazzar and Abu Yaala narrated it with a good chain." Ibn Hajar deemed the chain of Bazzar sound in Fath al-Bari (10/500).In the same meaning, it is reported from Abu Hurairah that he said, the Messenger of Allah ﷺ said, "Whoever visits a sick person, a caller calls out from the sky, 'You have been good, and your walk has been good, and you have taken up a dwelling in Paradise.'" This was narrated by Tirmidhi (2008), Ibn Majah (1443), Bukhari in Adab al-Mufrad (345), and Ibn Hibban (2961), all through the hadith of Abu Sinan Qasmali, who is Shami, from Uthman bin Abu Sawda, from Abu Hurairah, who mentioned it.Tirmidhi said, "This is a gharib hadith. Abu Sinan's name is Isa bin Sinan. Hammad bin Salama has narrated, from Thabit, from Abu Rafi, from Abu Hurairah, from the Prophet ﷺ, something similar to this." This Isa bin Sinan is daif, and Ibn Main, Abu Zura, Nasai, and others have judged him daif.