What are the prerequisites for the validity of the Adhan (call to prayer)?

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The Adhan is only valid if performed by a Muslim, sane, adult male. Infidels and the insane are excluded because they are not responsible for acts of worship. The Adhan of a woman is not recognized because she is not legislatively mandated to perform the Adhan, resembling the state of an insane person. Similarly, the Adhan of a hermaphrodite (Khuntha) is invalid because his gender status as male cannot be determined. This entire ruling is the position of Al-Shafi'i, and no opposing view is known concerning these prerequisites.