This issue, of claiming that the Qur’an is created, as you all are aware, is very serious. Great trial occured for Ahl As-Sunnah due to this issue, and at the head of (those who sustained great difficulty and tribulations was) Al-Imam Ahmed. During this trial, people were imprisoned, tortured, and killed. All of this was done by the Jahmiyah and the Mutazilah during the time of Al-Ma’mun, Al-Mu’tasim, and Al-Wathiq, during three different leaderships from the Abbasid Dynasty. The Islamic Ummah was put through a great trial by way of the Jahmiyah, the Mutazilah, and the other people of misguidance and deviation, where they gained power over the People of the Sunnah, but in the end Allaah decreed that the good end would be for His pious servants. Al Imam Ahmad exerted immense patience, persevering upon imprisonment, torture, and severe burdens that even the mountains would not be able to bare. So Allaah raised his level and his status, eventually becoming the Imam of Ahl As-Sunnah in truth.
Book: An explanation of Imam Ahmad’s foundations of the Sunnah – Shaykh Dr. Rabee ibn Haadee al-Madkhalee – Page 74