It is narrated from Sayyiduna Malik bin Amr bin Malik (may Allah be pleased with him); he said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever takes in an orphan from between two Muslim parents until he becomes self-sufficient, Allah has definitely made Paradise obligatory for him."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16718