Sunan Abi Dawud Book 2, Hadith 51

There is no remissness in sleep, it is only when one is awake that there is remissness when you delay saying the prayer till the time for the next prayer comes.

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"He performed ablution when the sun had arisen high and led them in prayer."

Sunan Abi Dawud Book 2, Hadith 50
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If any one forgets a prayer or oversleeps, he should observe it when he remembers it ; there is no expiation for it except that.

Sunan Abi Dawud Book 2, Hadith 52