When must the Tasmiyah (mentioning the name of God) be pronounced over an animal being slaughtered?

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The Tasmiyah upon slaughtering is considered valid if pronounced at the time of the actual cutting or very close to it, similar to its requirement for purification. If a person names God over one sheep and then takes another sheep to slaughter it using that same Tasmiyah, it is not permissible, whether the first sheep was released or slaughtered. This is because the intention of the Tasmiyah was not directed toward the second animal.