Sahih Muslim
The Book Pertaining to the Merits of the Companions (Allah Be Pleased With Them) of the Holy Prophet (May Peace Be Upon Him) (Kitab Al-Fadail Al-Sahabah)
Book Number: 031 / Hadith Number: 6010
Anas reported that Allah's Apostle (may peace be upon him) did not enter the house of any woman except that of his wives and that of Umm Sulaim. He used to visit her. It was said to him why it was so, whereupon he said: I feel great compassion for her. Her brother was killed while he was with me.