Shaykh al-Islaam Ibn Taymiyyah (rahimahullaah) stated as occurs in Majmu' al-Fatawa (6/215):
وأحمد إنما اشتهر أنه إمام أهل السنة ، والصابر على المحنة ، لما ظهرت محن [ الجهمية ] الذين ينفون صفات الله تعالى ، ويقولون إن الله لا يرى في الآخرة ، وأن القرآن ليس هو كلام الله تعالى ، بل هو مخلوق من المخلوقات .... وأضلوا بعض ولاة الأمر ، فامتحنوا الناس بالرغبة والرهبة ، فمن الناس من أجابهم رغبة ومن الناس من أجابهم رهبة ،ومنهم من اختفى فلم يظهر لهم ، وصار من لم يجبهم قطعوا رزقه وعزلوه عن ولايته ، والمحنة مشهورة معروفة ، كانت في إمارة المأمون ، والمعتصم ، والواثق ، ثم رفعها المتوكل ، فثبت الإمام أحمد ، فلم يوافقهم على تعطيل صفات الله تعالى ، وناظرهم في العلم فقطعهـم ، وعذبـوه فصبر على عذابهم ، فجعله الله من الأئمة الذين يهـدون بأمـره ، كما قال تعالى (وجعلنا منهم أئمة يهـدون بأمرنا لما صبروا وكانوا بآياتنا يوقنون) ، فمـن أعطي الصبر واليقين : جعـله الله إماماً في الدين
And Ahmad, it became widespread that he is the Imaam of Ahl al-Sunnah and the patient one upon tribulation when the trials of [Jahmites] appeared, those who negated the attributes of Allaah the Exalted and said "Allaah will not be seen in the Hereafter" and that "The Qur'an is not the speech of Allaah, the Exalted, but it is a creation from his creations" ... and they misguided some of those in authority and tested the people through aspiration (hope) and awe (fear). Thus, from the people were those who responded to them out of aspiration (hope) and from them were those who responded to them out of awe (fear) and from them were those who went into hiding and did not reveal himself to them. And they cut off the means of subsistence of whoever did not respond to them and removed him from his delegated position. And this tribulation is well-known and famous, it took place in the rulership of al-Ma'moon, al-Mu'tasim, al-Waathiq and then it was removed by al-Mutawakkil. So Imaam Ahmad remained firm and did not agree with them in negation of the attributes of Allaah, the Exalted, and he debated tehm with knowledge and cut them off. [As a result] they punished him and he showed patience over their punishment and thus Allaah made him from the leading Imaams, those who guide (others) by His command, just as the Exalted said, "And we made them to be Imaams (leaders), guiding by our command when they showed patience and had certainty in our signs." (32:24). Hence, whoever has been given patience and certainty, Allaah will make him an Imaam in the religion.
Imaam Ahmad bin Hanbal is the bridge to the aqidah of the Sahaabah after the Jahmites tried to sever the connection of the Ummah to them. And Imaam Ibn Taymiyyah is the bridge to the aqidah of the Salaf after the Ash'arites gained prominence between 500H to 700H and tore the Ummah away from them. Both were given Imaamah (leadership) in the religion.
Imaam Ahmad (rahimahullaah) was imprisoned and punished on account of a matter pertaining to tawhid, the claim that Allaah's speech (the Qur'aan) is created (a statement comprising kufr and shirk). Despite the tyranny and oppression of the rulers in this matter he was patient and also ordered others with patience and did not allow revolting or fighting against the rulers. This was in order to preserve the safety and security of the society at large. Ibn Taymiyyah likewise was imprisoned and put to trial by the Ash'arites of his time who had likewise influenced the rulers, and he was imprisoned on account of certain verdicts he gave which pertained to affairs connected to tawhid and its preservation. Both of these Ahmads (Ahmad bin Hanbal and Ahmed bin Abd al-Haleem) are Imaams of Ahl al-Sunnah, a matter that is famous and well-known, due to their aid of the deen of Islaam and tawhid of the Messengers.
We see the mighty difference in loftiness of purpose, honor and dignity between these great Imaams and those present today (Ikhwanis.Com), who, whilst idols are worshipped in their lands in the form of tombs of righteous saints and whilst the belief that the Qur'an is created is widespread amongst them, they mobilize the people against the rulers because of economic and political injustice (whose true and real causes they ignore, despite being made clear in the Qur'an and Sunnah), and they unite with the saint-worshippers, Rafidah Shi'ah, Jahmiyyah and others in the process. Then they clothe all of this activism under the label of establishing "Haakimiyyah," a great deception and fraud indeed. But more harmful (to Ahl al-Sunnah) than this is the condition of those ascribing to Salafiyyah (and to Imaam Ahmad and Ibn Taymiyyah) who accommodate those innovators in their da'wah and methodology, are sympathetic towards them and display greater love, affinity and loyalty towards them than the people of the Sunnah and Jamaa'ah. This is an act of treachery and indicates they do not have the love and loyalty to the aqidah of the Salaf they claim to have in their hearts, tongues and writings whilst their actions prove totally otherwise.
The Fitnah of the creation of the Qur'an has great lessons in methodology and da'wah and the Scholars of Sunnah and Salafiyyah have elaborated upon them to show the great difference between the methodologies of Ahl al-Sunnah in da'wah and rectification and the various innovated methodologies of da'wah and reform of the 20th century.