Sayyiduna Abu Umamah (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "Whoever washes a deceased person and conceals (his faults), Allah Almighty purifies that person of his sins; and if he shrouds him (that is, the deceased), Allah Almighty will clothe him in fine silk (sundus)."
Al-Tabarani recorded it in al-Mu'jam al-Kabir. Its chain contains a narrator, Abu Abdullah al-Shami, who narrated from Abu Khalid; I have not found anyone giving his biography.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجنائز / 4067