If he does it intentionally, his prayer is invalid.

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Reciting Surah Fateha is obligatory, the other Surah after that is a Sunnah whether in loud or silent prayers, including Imam. You will be missing out on the reward though if you skip the other Surah. The follower is not allowed to recite anything in loud rakah except the Fatiha. 

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1.Witr is not fard but rather a highly recommended sunnah which the Prophet salla Allahu aliaihi wa sallam never missed, even during safar. 2. Qunoot in Witr is not mandatory and it doesn’t require sujood as sahu if missed.

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