Al-Mu'jam al-Saghir

Sayyiduna Sa’d bin Hisham (may Allah be pleased with him) says: I asked Sayyidah Aisha (may Allah be pleased with her) about the night prayer of the Prophet (peace and blessings be upon him), so she said: When Allah the Exalted revealed this command: ﴿يَا أَيُّهَا الْمُزَّمِّلُ قُمِ اللَّيْلَ إِلَّا قَلِيلًا﴾ (Al-Muzzammil: 1-2) meaning, “O you who wraps himself [in clothing], stand [to pray] at night, except for a little,” then the night prayer became obligatory upon the Prophet (peace and blessings be upon him). This was the first obligation. The noble Companions (may Allah be pleased with them) also used to stand for prayer at night, until their feet became cracked. Then Allah the Exalted did not reveal the last part of this Surah for a year, then this verse was revealed: ﴿عَلِمَ أَنْ لَنْ تُحْصُوهُ فَتَابَ عَلَيْكُمْ فَاقْرَءُوا مَا تَيَسَّرَ مِنَ الْقُرْآنِ﴾ (Al-Muzzammil: 20) meaning, “Allah knows that you cannot keep it up, so He has turned to you in mercy, so recite what is easy [for you] of the Qur’an.” Thus, the night prayer became voluntary.