What is the legal status of an abandoned infant found in a land previously Muslim but now overcome by non-believers (e.g., the coast)?

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If a single Muslim is present in a territory previously Muslim but currently dominated by non-believers, the infant found there is ruled a Muslim, presuming affiliation with the existing Muslim. If no Muslim is present, the infant is ruled a disbeliever. The Qadi holds that the infant should be ruled a Muslim even without a present Muslim, presuming a hidden believer, distinguishing this case from conquered lands where inhabitants are openly Ahl al-Dhimma and have no need to conceal their faith in Dar al-Islam. This detailed differentiation is attributed to the Shafi'i school.