Sahih al-Bukhari 4927
Sahih al-Bukhari · Book 65: Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh)) · The Statement of Allah the Exalted: "Move not your tongue concerning (the Qur'an, O Muḥammad pbuh) to make haste therewith." (V.75:16)
Narrated Ibn `Abbas:
حَدَّثَنَا الْحُمَيْدِيُّ ، حَدَّثَنَا سُفْيَانُ ، حَدَّثَنَا مُوسَى بْنُ أَبِي عَائِشَةَ ـ وَكَانَ ثِقَةً ـ عَنْ سَعِيدِ بْنِ جُبَيْرٍ ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ كَانَ النَّبِيُّ صلى الله عليه وسلم إِذَا نَزَلَ عَلَيْهِ الْوَحْىُ حَرَّكَ بِهِ لِسَانَهُ ـ وَوَصَفَ سُفْيَانُ ـ يُرِيدُ أَنْ يَحْفَظَهُ فَأَنْزَلَ اللَّهُ {لاَ تُحَرِّكْ بِهِ لِسَانَكَ لِتَعْجَلَ بِهِ}
The Prophet (ﷺ) used to move his tongue when the divine Inspiration was being revealed to him. (Sufyan, a subnarrator, demonstrated (how the Prophet (ﷺ) used to move his lips) and added. "In order to memorize it." So Allah revealed: "Move not your tongue concerning (the Qur'an) to make haste therewith." (75.16)