Musnad Abu Ya'la al-Mawsili 155:15

Muhammad ibn al-Minhal, the brother of Hajjaj, narrated to us, [saying]: Abd al-Wahid narrated to us, from Ma'mar, from al-Zuhri, from Sa'id ibn al-Musayyib, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "If Allah intends good for a servant, He grants him understanding of the religion." And he said: "I am only a distributor, and Allah is the One who gives."