question #2 Sahih Muslim 755a, Book 6, Hadith 195 : Why is the prayer at the end of the night considered preferable and witnessed by angels?

If anyone is afraid that he may not get up in the latter part of the night, he should observe Witr in the first part of it; and if anyone is eager to get up in the last part of it, he should observe Witr at the end of the night, for prayer at the end of the night is witnessed (by the angels) and that is preferable.