Sahih Bukhari Volume 6, Book 65, Hadith 4931

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا جَرِيرٌ، عَنْ مُوسَى بْنِ أَبِي عَائِشَةَ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ، فِي قَوْلِهِ ‏{‏لاَ تُحَرِّكْ بِهِ لِسَانَكَ لِتَعْجَلَ بِهِ‏}‏ قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا نَزَلَ جِبْرِيلُ بِالْوَحْىِ، وَكَانَ مِمَّا يُحَرِّكُ بِهِ لِسَانَهُ وَشَفَتَيْهِ فَيَشْتَدُّ عَلَيْهِ وَكَانَ يُعْرَفُ مِنْهُ، فَأَنْزَلَ اللَّهُ الآيَةَ الَّتِي فِي ‏{‏لاَ أُقْسِمُ بِيَوْمِ الْقِيَامَةِ‏}‏ ‏{‏لاَ تُحَرِّكْ بِهِ لِسَانَكَ لِتَعْجَلَ بِهِ * إِنَّ عَلَيْنَا جَمْعَهُ وَقُرْآنَهُ‏}‏ قَالَ عَلَيْنَا أَنْ نَجْمَعَهُ فِي صَدْرِكَ، وَقُرْآنَهُ ‏{‏فَإِذَا قَرَأْنَاهُ فَاتَّبِعْ قُرْآنَهُ‏}‏ فَإِذَا أَنْزَلْنَاهُ فَاسْتَمِعْ ‏{‏ثُمَّ إِنَّ عَلَيْنَا بَيَانَهُ‏}‏ عَلَيْنَا أَنْ نُبَيِّنَهُ بِلِسَانِكَ ـ قَالَ ـ فَكَانَ إِذَا أَتَاهُ جِبْرِيلُ أَطْرَقَ، فَإِذَا ذَهَبَ قَرَأَهُ كَمَا وَعَدَهُ اللَّهُ‏.‏ ‏{‏أَوْلَى لَكَ فَأَوْلَى‏}‏ تَوَعُّدٌ‏.

Narrated By Ibn Abbas : (As regards) Allah's Statement: "Move not your tongue concerning (the Qur'an) to make haste therewith." (75.16) When Gabriel revealed the Divine Inspiration in Allah's Apostle , he (Allah's Apostle) moved his tongue and lips, and that state used to be very hard for him, and that movement indicated that revelation was taking place. So Allah revealed in Surat Al-Qiyama which begins: 'I do swear by the Day of Resurrection...' (75) the Verses: 'Move not your tongue concerning (the Qur'an) to make haste therewith. It is for Us to collect it (Qur'an) in your mind, and give you the ability to recite it by heart. (75.16-17) Ibn Abbas added: It is for Us to collect it (Qur'an) (in your mind), and give you the ability to recite it by heart means, "When We reveal it, listen. Then it is for Us to explain it," means, 'It is for us to explain it through your tongue.' So whenever Gabriel came to Allah's Apostle ' he would keep quiet (and listen), and when the Angel left, the Prophet would recite that revelation as Allah promised him.