The Messenger of Allah ﷺ used to undergo great strain when revelation came down, and among the signs of it was that he would move his lips.Ibn Abbas said, "I will move my lips for you the way the Messenger of Allah ﷺ used to move his."Saeed said, "And I will move mine the way I saw Ibn Abbas move his," and he moved his lips.Then Allah Most High revealed, "Do not move your tongue with it to hasten it. It is upon Us to gather it and to recite it" [Qiyamah 75:16–17].Ibn Abbas explained, "It means He will gather it for you in your breast, and you will recite it." Then, "So when We have recited it, follow its recitation." He said, "That is, listen to it and be silent." Then, "Then it is upon Us to make it clear," meaning it is upon Us that you recite it.After that, whenever Jibreel came to the Messenger of Allah ﷺ, he would listen, and once Jibreel departed, the Prophet ﷺ would recite it just as Jibreel had recited it.
في قوله تعالى: {لا تحرك به لسانك لتعجل به} [القيامة: ١٦]
كان رسول الله ﷺ يعالج من التنزيل شدة وكان مما يحرك شفتيه، فقال ابن عباس: فأنا أحركهما لكم كما كان رسول الله ﷺ يحركهما. وقال سعيد: أنا أحركهما كما رأيت ابن عباس يحركهما-فحرك شفتيه- فأنزل الله تعالى: {لا تحرك به لسانك لتعجل به إن علينا جمعه وقرءانه} [سورة القيامة: ١٦-١٧] قال: جمعه لك في صدرك وتقرأه {فإذا قرأنه فاتبع قرءانه} قال: فاستمع له وأنصت {ثم إن علينا بيانه} ثم إن علينا أن تقرأه. فكان رسول الله ﷺ بعد ذلك إذا أتاه جبريل استمع، فإذا انطلق جبريل قرأه النبي ﷺ كما قرأه.
Bukhari narrated it in the Book of the Beginning of Revelation (5), and Muslim in the Book of Prayer (448), both from the hadith of Abu Awana, from Musa bin Abu Ayesha, from Saeed bin Jubayr, from Ibn Abbas, as mentioned. The wording given is Bukhari's, and Muslim did not mention Ibn Abbas moving his lips, nor what follows it.