Hadith: The Prophet (may Allah's peace and blessings be upon him) used to experience hardship while the revelation was being sent down upon him, and he used to move his lips (quickly) with what was being revealed to him

عن ابن عباس رضي الله عنهما في قوله تعالى: {لا تُحَرِّكْ به لسانَك} [القيامة: 16]، قال: «كان النبيُّ صلى الله عليه وسلم يُعالِجُ مِن التنزيل شِدَّةً، وكان يُحَرِّكُ شَفَتَيْهِ» فقال لي ابنُ عباس: فأنا أُحَرِّكُهما لك كما كان رسولُ الله صلى الله عليه وسلم يُحَرِّكُهما، فقال سعيد: أنا أُحَرِّكُهما كما كان ابنُ عباس يُحَرِّكُهما، فحرَّك شَفَتَيْهِ فأنزل اللهُ -عزَّ وجلَّ-: {لا تُحَرِّكْ به لسانَك لِتَعْجَلَ به إنَّ علينا جَمْعَه وقُرآنَه} [القيامة: 17]، قال: «جَمْعَه في صدرك ثم تقرؤه»، {فإذا قرأناه فاتَّبِعْ قُرآنه} [القيامة: 18] قال: «فاستمِع له وأَنْصِتْ، ثم إنَّ علينا أن تقْرَأه، قال: فكان رسول الله صلى الله عليه وسلم إذا أتاه جبريل عليه السلام استمع، فإذا انطلقَ جبريلُ قرأه النبي صلى الله عليه وسلم كما أقرَأَه».
[صحيح] - [متفق عليه]

Ibn ‘Abbās (may Allah be pleased with him) commented about the verse: {Move not your tongue with it, [O Muhammad], to hasten with recitation of the Qur'an} [Sūrat al-Qiyāmah: 16], saying: "The Prophet (may Allah's peace and blessings be upon him) used to experience hardship while the revelation was being sent down upon him, and he used to move his lips (quickly) with what was being revealed to him." Ibn ‘Abbās moved his lips saying: "I am moving my lips in front of you as the Messenger of Allah (may Allah's peace and blessings be upon him) used to move his." Sa‘īd (the sub-narrator) also moved his lips saying: "I am moving my lips just as I saw Ibn ‘Abbās moving his." Ibn ‘Abbās added: "So Allah revealed the following verses: {Move not your tongue with it, [O Muhammad], to hasten with recitation of the Qur'an. Indeed, upon Us is its collection [in your heart] and [to make possible] its recitation.} [Sūrat al-Qiyāmah: 16-17] which means that Allah will make him (the Prophet) remember the portion of the Qur'an which was revealed to him at that time by heart and recite it. Then the verse that followed these two was: {So when We have recited it [through Jibrīl], then follow its recitation} [Sūrat al-Qiyāmah: 18] It means ''listen to it and be silent. Then, it is (for Allah) to make you recite it." Afterwards, the Messenger of Allah (may Allah's peace and blessings be upon him) used to listen to Jibrīl whenever he came to him, and after his departure he used to recite it just as Jibrīl taught him to recite it."
[Authentic hadith] - [Narrated by Bukhari & Muslim]

Explanation

Ibn ‘Abbās (may Allah be pleased with him) says that the Prophet (may Allah's peace and blessings be upon him) used to experience hardship and intense stress while the revelation was being sent down upon him. He used to move his lips with what he received from Jibrīl before Jibrīl had finished the revelation, fearing that he would not be able to memorize it before Jibrīl left. Ibn ‘Abbās described to his student Sa‘īd ibn Jubayr how the Prophet moved his lips. This indicates that Ibn ‘Abbās had seen the Prophet in that state. Sa‘īd, likewise, described it to his students. Allah, the Exalted, sent down a verse commanding the Prophet not to move his tongue with the Qur'an to hasten in receiving it, for Allah ensured that the Qur'an would be collected in the Prophet's heart. Then, Allah, the Almighty, revealed another verse telling the Prophet to listen attentively when Jibrīl recited the Qur'an to him, for Allah ensured that the Prophet would recite it just as Jibrīl had recited it. Later on, when Jibrīl came to the Prophet with revelation, the Prophet would listen to him, and when Jibrīl had departed, the Prophet would read the Qur'an as Jibrīl taught him to read it.