Musnad Ahmad 1153:896

'Affan narrated to us, he said: 'Abd al-Wahid ibn Ziyad narrated to us, he said: al-Hasan ibn 'Ubayd Allah narrated to us, he said: Ibrahim narrated to us, from al-Aswad ibn Yazid, from 'A'ishah, she said: "The Messenger of Allah, peace and blessings of Allah be upon him, used to exert himself during the ten [last days of Ramadan] in a way that he did not exert himself in other [times]."