Musnad Ahmad 1153:895

'Affan narrated to us, Hammad ibn Salamah narrated to us, he said: Hisham informed us, from 'Urwah, from 'Aishah, that some people were performing intense worship, so the Prophet, peace and blessings of Allah be upon him, forbade them. He said: "By Allah, I am the most knowledgeable of you regarding Allah, the Almighty and Majestic, and the most fearful of Him." And he used to say: "Take upon yourselves of deeds that which you can endure, for Allah, the Almighty and Majestic, does not grow weary until you grow weary."