Language:
كتاب الوصايا
55  
Wills and Testaments (Wasaayaa)
(22)
Chapter: How a guardian is to deal with an orphan's wealth
(22)
باب وَمَا لِلْوَصِيِّ أَنْ يَعْمَلَ فِي مَالِ الْيَتِيمِ، وَمَا يَأْكُلُ مِنْهُ بِقَدْرِ عُمَالَتِهِ
Sahih al-Bukhari 2765

Narrated `Aisha:

The following Verse:-- "If a guardian is well-off, let him claim no remuneration (i.e. wages), but if he is poor, let him have for himself what is just and reasonable." (4.6) was revealed in connection with the guardian of an orphan, and it means that if he is poor he can have for himself (from the orphan's wealth) what is just and reasonable according to the orphan's share of the inheritance.

حَدَّثَنَا عُبَيْدُ بْنُ إِسْمَاعِيلَ، حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ هِشَامٍ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ ـ رضى الله عنها – ‏{‏وَمَنْ كَانَ غَنِيًّا فَلْيَسْتَعْفِفْ وَمَنْ كَانَ فَقِيرًا فَلْيَأْكُلْ بِالْمَعْرُوفِ‏}‏‏.‏ قَالَتْ أُنْزِلَتْ فِي وَالِي الْيَتِيمِ أَنْ يُصِيبَ مِنْ مَالِهِ إِذَا كَانَ مُحْتَاجًا بِقَدْرِ مَالِهِ بِالْمَعْرُوفِ‏.‏
Reference : Sahih al-Bukhari 2765
In-book reference : Book 55, Hadith 28
USC-MSA web (English) reference : Vol. 4, Book 51, Hadith 27
  (deprecated numbering scheme)