Ikrimah narrates from Sayyiduna Ibn Abbas (may Allah be pleased with him) that he said: "The guardian may eat from the orphan's wealth with his fingers, but no more than that (that is, not to increase his own wealth, but only to satisfy his hunger)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10998