Asma' bint Umays (may Allah be pleased with her) narrates that Fatimah, the daughter of the Messenger of Allah (peace and blessings be upon him), left instructions that her husband, Ali bin Abi Talib (may Allah be pleased with him), should wash her. So it was Ali (may Allah be pleased with him) and Asma' bint Umays (may Allah be pleased with her) who washed her.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6661