Abdullah bin Abbas reported,

Regarding Surah al-Muzzammil, the verse "Stand in prayer through the night, except for a little, half of it" [Muzzammil 73:2–3] was abrogated by the verse in the same surah, "He knows that you will not be able to maintain it, so He has turned to you in mercy. Therefore recite whatever is easy of the Quran" [Muzzammil 73:20].The "rising of the night" refers to its beginning, for they used to pray during the early part of the night. He is saying that this is more conducive to your fulfilling what Allah has imposed upon you of standing in prayer at night. This is because when a person sleeps, he does not know when he will wake up.As for His saying "more upright in speech" [Muzzammil 73:6], it means it is more conducive to understanding the Quran.And His saying "Indeed, for you during the day is prolonged occupation" [Muzzammil 73:7] means a long span of free time.

حدثنا أحمد بن محمد المروزي ابن شبويه حدثني علي بن حسين عن أبيه عن يزيد النحوي عن عكرمة

عن ابن عباس قال

في المزمل {قم الليل إلا قليلا نصفه} نسختها الآية التي فيها {علم أن لن تحصوه فتاب عليكم فاقرءوا ما تيسر من القرآن} وناشئة الليل أوله وكانت صلاتهم لأول الليل يقول هو أجدر أن تحصوا ما فرض الله عليكم من قيام الليل وذلك أن الإنسان إذا نام لم يدر متى يستيقظ وقوله أقوم قيلا هو أجدر أن يفقه في القرآن وقوله {إن لك في النهار سبحا طويلا} يقول فراغا طويلا