From Sahih Bukhari (Hadith 4575):
Narrated Aisha:regarding the Statement of Allah: "And whoever amongst the guardian is rich, he should take no wages, but if he is poor, let him have for himself what is just and reasonable (according to his work). This Verse was revealed regarding the orphan's property. If the guardian is poor, he can take from the property of the orphan, what is just and reasonable according to his work and the time he spends on managing it
Reference: Bukhari 4575