The Prophet (may Allah's peace and blessings be upon him) used to experience hardship while the revelation was being sent down upon him, and he used to move his lips (quickly) with what was being revealed to him

Ibn ‘Abbās (may Allah be pleased with him) says that the Prophet (may Allah's peace and blessings be upon him) used to experience hardship and intense stress while the revelation was being sent down upon him. He used to move his lips with what he received from Jibrīl before Jibrīl had finished the revelation, fearing that he would not be able to memorize it before Jibrīl left. Ibn ‘Abbās described to his student Sa‘īd ibn Jubayr how the Prophet moved his lips.

This indicates that Ibn ‘Abbās had seen the Prophet in that state. Sa‘īd, likewise, described it to his students. Allah, the Exalted, sent down a verse commanding the Prophet not to move his tongue with the Qur'an to hasten in receiving it, for Allah ensured that the Qur'an would be collected in the Prophet's heart.

Then, Allah, the Almighty, revealed another verse telling the Prophet to listen attentively when Jibrīl recited the Qur'an to him, for Allah ensured that the Prophet would recite it just as Jibrīl had recited it. Later on, when Jibrīl came to the Prophet with revelation, the Prophet would listen to him, and when Jibrīl had departed, the Prophet would read the Qur'an as Jibrīl taught him to read it.