Musnad Ahmad 1153:310

Abu Usamah narrated to us, he said: Hisham informed us, from his father, from Aisha, who said: The Messenger of Allah (peace and blessings of Allah be upon him) used to command them to do what they were capable of. They would say: "We are not like you; Allah the Almighty has forgiven you your past and future sins." He would then become angry until that was visible on his face. He would say: "By Allah, I am the most knowledgeable of you regarding Allah the Almighty, and the most fearful of Him in heart."