Mishkat al-Masabih
Thauban reported God’s messenger as saying, “When a Muslim pays a sick visit to his brother Muslim he continues to gather the fruits of paradise till he returns.” Muslim transmitted it.
وَعَنْ ثَوْبَانَ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِنَّ الْمُسْلِمَ إِذَا عَادَ أَخَاهُ الْمُسلم لم يزل فِي خُرْفَةِ الْجَنَّةِ حَتَّى يَرْجِعَ» . رَوَاهُ مُسْلِمٌ
Reference