Language:
كتاب الجهاد والسير
56  
Fighting for the Cause of Allah (Jihaad)
(38)
Chapter: The superiority of the one who prepares a Ghazi or looks after his dependents
(38)
باب فَضْلِ مَنْ جَهَّزَ غَازِيًا أَوْ خَلَفَهُ بِخَيْرٍ
Sahih al-Bukhari 2844

Narrated Anas:

The Prophet (ﷺ) used not to enter any house in Medina except the house of Um Sulaim besides those of his wives when he was asked why, he said, "I take pity on her as her brother was killed in my company. "

حَدَّثَنَا مُوسَى، حَدَّثَنَا هَمَّامٌ، عَنْ إِسْحَاقَ بْنِ عَبْدِ اللَّهِ، عَنْ أَنَسٍ ـ رضى الله عنه ـ أَنَّ النَّبِيَّ صلى الله عليه وسلم لَمْ يَكُنْ يَدْخُلُ بَيْتًا بِالْمَدِينَةِ غَيْرَ بَيْتِ أُمِّ سُلَيْمٍ، إِلاَّ عَلَى أَزْوَاجِهِ فَقِيلَ لَهُ، فَقَالَ ‏ "‏ إِنِّي أَرْحَمُهَا، قُتِلَ أَخُوهَا مَعِي ‏"‏‏.‏
Reference : Sahih al-Bukhari 2844
In-book reference : Book 56, Hadith 60
USC-MSA web (English) reference : Vol. 4, Book 52, Hadith 97
  (deprecated numbering scheme)