Musnad Ahmad 1153:893

'Affan narrated to us, he said: Salam ibn Abi Muti' narrated to me, from Jabir, from al-Sha'bi, from Yahya ibn al-Jazzar, he said: 'Aisha said: "Whoever washes a deceased person and fulfills the trust therein"—meaning that he does not disclose what he sees from him during that—"he shall be [cleansed] of his sins like the day his mother gave birth to him." She said: And the Messenger of Allah (peace and blessings of Allah be upon him) said: "And let his closest family member wash him if he has knowledge [of how to do so]. If he does not have knowledge, then let him be washed by one of you whom you see as having a share of piety or trustworthiness."