Musnad Ahmad 962:17

Abu Ishaq al-Taliqani narrated to us, Abdullah ibn al-Mubarak narrated to us, from Yahya ibn Ayyub, from Ubayd Allah ibn Zahr, from Ali ibn Yazid, from al-Qasim, from Abu Umamah, that the Messenger of Allah, peace and blessings of Allah be upon him, said: "Whoever strokes the head of an orphan, not stroking it except for the sake of Allah, will have for every hair that his hand passes over, good deeds. And whoever treats well an orphan girl or an orphan boy who is with him, I and he will be in Paradise like these two," and he joined his two fingers, the index and the middle.