Musnad Ahmad

It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) regarding the interpretation of the Quranic verse: « ﴿لَا تُحَرِّكْ بِهِ لِسَانَكَ لِتَعْجَلَ بِهِ﴾ [القيامة : 16]» "Do not move your tongue quickly," that the Prophet (peace and blessings be upon him) used to feel some difficulty at the time of the revelation of the divine message, and in order to preserve the revelation, he would keep moving his lips. Saying this, Sayyiduna Ibn Abbas (may Allah be pleased with them both) said to his student Sa'id bin Jubair (may Allah have mercy on him), "I will show you how the Prophet (peace and blessings be upon him) used to move his lips," and then his student Sa'id bin Jubair (may Allah have mercy on him) imitated this in front of his own student. In any case, upon this, the following verse was revealed: «﴿لَا تُحَرِّكْ بِهِ لِسَانَكَ لِتَعْجَلَ بِهِ o إِنَّ عَلَيْنَا جَمْعَهُ وَقُرْآنَهُ o فَإِذَا قَرَأْنَاهُ فَاتَّبِعْ قُرْآنَهُ o ثُمَّ إِنَّ عَلَيْنَا بَيَانَهُ﴾ [القيامة : 16-19]» "Do not move your tongue quickly; it is Our responsibility to gather this Quran in your chest and to make you recite it. So when We recite it, listen to it attentively and remain silent; then its explanation is also Our responsibility." After this, the Prophet (peace and blessings be upon him) would recite it in the same way after Jibreel (peace be upon him) had departed, as Jibreel (peace be upon him) had recited it to the Prophet (peace and blessings be upon him).