It should be noted that the only conditions for a Nikkah to be deemed valid and complete are the "Eijab" (offer) and "Qubool" (acceptance) and the presence of 2 witnesses. According to Shariah, it is not mandatory for the Qazi to make the groom recite the 6 kalimas at the time of Nikkah. This practice likely arose because, due to ignorance, people sometimes utter blasphemous words without realizing that such utterances can take them out of the fold of Islam. Therefore, the groom is made to recite the Kalimas before the Nikah to ensure that if such a situation has occurred, the groom can reaffirm their faith. Nonetheless, in general circumstances, it is not necessary to recite the Kalimas before the Nikah, though there is no harm if it is done occasionally.
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دلائل:
الدر المنتقی: (کتاب النکاح، 467/1، ط: دار الکتب العلمیۃ)
ہو (النکاح) لغۃ الضم والجمع وشرعًا عقد مجموع إیجاب وقبول ولو حکما یرد علی ملک المتعۃ أي حل استمتاع الرجل من المرأۃ قصدًا (إلی قولہ) وشرط لصحۃ العقد المذکور سماع کل من العاقدین لفظ الآخر … وحضور شاہدین حرین أو حر وحرتین مکلفین أي عاقلین بالغین۔
Allah the Almighty knows best.
Darul ifta Al-Ikhlas, Karachi.