Musnad Ahmad 1153:1096

Yazid narrated to us, Hammad ibn Salamah informed us, from Hammad, from Ibrahim, from al-Aswad, from Aisha, that the Messenger of Allah (may Allah bless him and grant him peace) said: "The pen is lifted from three: from the sleeper until he wakes up, from the afflicted until he recovers, and from the child until he reaches understanding."