Can he say du ‘aa’ between the two prostrations in words other than those narrated from the Prophet (blessings and peace of Allah be upon him)?

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Check below answers in case you are looking for other related questions:
Ruling on the takbeers of movement (in the prayer) and the du‘aa’ between the two prostrations
Ruling on wearing shirts with writing on them when praying

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Ruling on the takbeers of movement (in the prayer) and the du‘aa’ between the two prostrations
Ruling on wearing shirts with writing on them when praying

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