ANSWER: It is a form of transgression as the Prophet salla allahu alaihi wa sallam told the companions that he prays and sleeps and that whoever follows other than his sunnah, he is not from him. 

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ANSWER: This is a major sin and some scholars consider this apostasy and that this person is now out of the fold of Islam. https://islamqa.info/en/answers/5208/neglecting-prayer-out-of-laziness

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ANSWER: You should pray witr and sleep and if you wake up for tahajjud then you should pray in even numbers and not repeat the witr as witr is prayed only once per night.

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