The Book on Salutations and Greetings (Kitab As-Salam)
Muslim :: Book 26 : Hadith 5403
'Abdullah b. 'Amr. b. al-'As reported that some persons from Banu Hisham entered the house of Asma' daughter of 'Umais when Abu Bakr also entered (and she was at that time his wife). He (Abu Bakr) saw it and disapproved of it and he made a mention of that to Allah's Messenger (may peace be upon him) and said: I did not see but good only (in my wife). Thereupon Allah's Messenger (may peace be upon him) said: Verily Allah has made her immune from all this. Then Allah's Messenger (may peace be upon him) stood on the pulpit and said: After this day no man should enter the house of another person in his absence, but only when he is accompanied by one person or two persons.