Hadith 4:65
Anas said the Prophet was not accustomed to visit an invalid till he had been ill for three days. Ibn Majah and Baihaqi, in Shu'ab al- iman , transmitted it.
وَعَنْ أَنَسٍ قَالَ: كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ لَا يَعُودُ مَرِيضًا إِلَّا بَعْدَ ثَلَاثٍ. رَوَاهُ ابْنُ مَاجَهْ وَالْبَيْهَقِيُّ فِي شُعَبِ الْإِيمَانِ
Original Reference: Mishkat al-Masabih 1587