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)
كَانَ النَّبِيُّ ﷺ إِذَا نَزَلَ عَلَيْهِ الْوَحْىُ حَرَّكَ بِهِ لِسَانَهُ وَوَصَفَ سُفْيَانُ يُرِيدُ أَنْ يَحْفَظَهُ فَأَنْزَلَ اللَّهُ {لاَ تُحَرِّكْ بِهِ لِسَانَكَ لِتَعْجَلَ بِهِ}
“When the Quran was being revealed to the Messenger of Allah, he would move his tongue in attempt to memorize it. So Allah, Blessed is He and Most High, revealed: Move not your tongue concerning it to make haste therewith.” He said: “So he would move his two lips.” And Sufyan (a sub-narrator) would move his two lips.
كَانَ رَسُولُ اللَّهِ ﷺ إِذَا أُنْزِلَ عَلَيْهِ الْقُرْآنُ يُحَرِّكُ بِهِ لِسَانَهُ يُرِيدُ أَنْ يَحْفَظَهُ فَأَنْزَلَ اللَّهُ ( لا تُحَرِّكْ بِهِ لِسَانَكَ لِتَعْجَلَ بِهِ ) قَالَ فَكَانَ يُحَرِّكُ بِهِ شَفَتَيْهِ وَحَرَّكَ سُفْيَانُ شَفَتَيْهِ