What is the ruling on washing the deceased? If a body is buried without being washed, should it be exhumed and washed?

Washing and shrouding a Muslim's body is a communal obligation (fard kifayah). (Kâsânî, Bedâ’i, 1/300, 306, 318; Mevsılî, el-İhtiyâr, 1/91-93) If some Muslims fulfill this duty, the responsibility is lifted from the rest. If, for any reason, a body is buried without being washed, it should not be exhumed for washing after the burial is completed. (Ibn Abidin, Reddü’l-muhtâr, 2/207-208)

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu