Ali narrated from his father, from Hammad ibn Isa, from Hariz, from Muhammad ibn Muslim, who said:
I asked Imam عليه السلام about a man washing his wife. Imam عليه السلام said: "Yes (it is allowed), (it is) only her family prevents it out of prejudice."
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 1, p. 465