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.
Bukhari
Wills and Testaments (Wasaayaa) • Hadith 28