If he missed them without a legit reason, he cannot make them up. If he had a valid reason, he prays them as the order goes (asr, maghrib, isha).

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If you realized that you are in the 5th, you must immediately sit for tashahud without continuing the 5th. You must offer Salam after the two forgetfulness sujood. However, due to your ignorance, your prayer is valid.

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The prayer is valid if you do not hold or fold your hands but you lose reward for not following the sunnah.

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