If anyone fears that he will not wake up at the end of the night, let him offer Witr prayer at the beginning of the night; and anyone expects to wake up at the end of the night, let him offer Witr prayer at the end of the night. Indeed, prayer at the end of the night is witnessed (by the angels) and that is better
Chapter: One who fears that he will not get up at the end of the night, then he should pray Witr at the beginning of the night
Authentic
hadith of Sahih Muslim
Sahih Muslim 755a
Jābir (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "If anyone fears that he will not wake up at the end of the night, let him offer Witr prayer at the beginning of the night; and anyone expects to wake up at the end of the night, let him offer Witr prayer at the end of the night. Indeed, prayer at the end of the night is witnessed (by the angels) and that is better."
The Hadīth indicates that it is permissible for the Muslim to pray Witr at the beginning of the night, especially for the one who fears that he will not wake up at the end of the night. It also emphasizes the preference of offering Witr prayer at the end of the night because it is witnessed by the angels.
Explanation in Arabic
يبين الحديث جواز صلاة الوتر في أول الليل، ويكون الجواز أولى في حق من خشي ألا يقوم آخر الليل، كما بين أفضلية صلاته في آخر الليل وذلك لكونها مشهودة من الملائكة.
أنَّ الوتر يجوز في أول الليل وفي آخره، فوقته من صلاة العشاء إلى طلوع الفجر الثاني، ومن كل الليل أوتر النبي -صلى الله عليه وسلم-.
أنَّ تأخير الوتر إلى آخر الليل أفضل لمن قوي على القيام، وطمع في أن يستيقظ قبل الفجر.
أنَّ من يخشى ألا يقوم آخر الليل؛ يشرع له الوتر قبل أن ينام, ويكون في حقه أفضل.