Al-Qiyamah 75:18

As narrated from Ibn Abbas in Bukhari and Muslim, while revelation was coming down the Prophet would move his tongue and lips, repeating hastily for fear of forgetting; this was a strain upon him. Thereupon the verses were revealed: "Do not move your tongue with it to hasten it. Surely upon Us is its collection and its recitation. So when We recite it, follow its recitation." From then on, the Prophet would listen to Gabriel in silence and recite it as he had heard once Gabriel departed.

Buhârî 5; Müslim 448

Surah al-Qiyama is Meccan. It answers the Meccans who denied resurrection by asking how decayed bones could be revived, declaring that God is able to reshape even the fingertips. As related from Ibn Abbas in Bukhari, the verses 'Do not move your tongue with it to hasten it' were revealed when the Prophet, anxious not to forget the revelation, would repeat it along with Gabriel, and they affirmed that securing it in his memory belongs to God.

Buhârî rivayeti (İbn Abbas hadisi); klasik tefsir mukaddimeleri