Sayyidah Aishah (may Allah be pleased with her) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Whoever takes charge of washing a deceased person should fulfil the trust in it, that is, conceal whatever there is in it; he will become as pure of his sins as though his mother had given birth to him today." The Messenger of Allah (peace and blessings be upon him) said: "The one in charge of it should be his closest relative, if he knows (how); if his closest relative does not know, then someone about whom you know that he will take care of the trust."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6658