What is the ruling for washing and praying over an unknown deceased person found in a Muslim land?

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If a deceased person is found and it is unknown whether they were Muslim or Kafir (unbeliever), one must examine distinguishing marks such as circumcision, clothing, or dyeing (Khadab). If no distinguishing mark is present and the body is found within the territory of Islam (Dar al-Islam), the deceased must be washed and the funeral prayer (Salat al-Janazah) must be performed over them. This is because the default ruling is that whoever is in a land is considered among its inhabitants, and the ruling of that land applies to them unless evidence proves otherwise. This ruling is stated by Ahmad.