He started to pray, then he wasn’t sure whether he formed the intention to pray or not; does he have to repeat it?

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Check below answers in case you are looking for other related questions:
Remedy for Insinuating Whispers that has to do with Purification and Prayer
Remedy for Whispers from Shaytan

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Related Answers:
If the imam stands up for an extra rak’ah, what should the one who is praying behind him do?
What should be said in the two prostrations of forgetfulness and in between them?
In doubt concerning the number of raka’at that have been prayed
Remedy for Insinuating Whispers that has to do with Purification and Prayer
Remedy for Whispers from Shaytan

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