In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Bahlool [may Allaah have mercy upon him] wrote to Al-Waathiq (1) [may Allaah have mercy upon him]: Indeed, a pretentious person has jested with your religion, desires have surrounded you, the statements of the proponents of religious innovations have deprived you of sound reasoning and Ibn Abee Du’aad – the sinister one – has changed the words of your Lord. Read the statement of Allaah (when he said to Moosaa):
فَٱخۡلَعۡ نَعۡلَيۡكَۖ إِنَّكَ بِٱلۡوَادِ ٱلۡمُقَدَّسِ طُوً۬ى
وَأَنَا ٱخۡتَرۡتُكَ فَٱسۡتَمِعۡ لِمَا يُوحَىٰٓ
إِنَّنِىٓ أَنَا ٱللَّهُ لَآ إِلَـٰهَ إِلَّآ أَنَا۟ فَٱعۡبُدۡنِى وَأَقِمِ ٱلصَّلَوٰةَ لِذِڪۡرِىٓ
So take off your shoes, you are in the sacred valley, Tuwa. “And I have chosen you. So listen to that which is inspired to you. “Verily! I am Allah! La ilaha illa Ana (none has the right to be worshipped but I), so worship Me, and perform As-Salat (Iqamat-as-Salat) for My Remembrance. [Surah Taa Haa. Aayaat 12-14]
So, can this speech be something created? May Allaah send upon you Sijjeel [stones of backed clay] marked by your Lord and they are not ever far from the wrong doers.
Then he concluded the letter as follows:
From the one who is fearful and is of low status to the one who opposes the speech of his Lord [The Exalted].
Bahlool [may Allaah have mercy upon him] also wrote to Ibn Abee Du’aad (2) as follows:
Indeed, you have separated Allaah’s Speech from Him and claim that it is created. If what you have stated is false, then may Allaah send a calamity upon you. Woe to you! Were you with Allaah when He spoke to Moosaa? If you reject this, then read the speech of Allaah:
أُوْلَـٰٓٮِٕكَ هُمُ ٱلۡكَفَرَةُ ٱلۡفَجَرَةُ
And other faces, that Day, will be dust-stained; darkness will cover them, such will be the disbelievers and wicked evil doers. [Surah Abasa. Aayaat 40-42]
Then he ended the letter as follows:
From a truthful and humble person to a liar and a haughty one.
[An Excerpt from Uqalaa Al-Majaaneen. Page 40. Slightly paraphrased]
Ref 1: NB: Al-Waathiq Ameerul Mumineen [may Allaah have mercy upon him] was misled by the Mutazilah, especially Ibn Abee Du’aad, but he repented from the Bidah that the Qur’aan is created before he died. [See Siyar A’laam An-Nubulaa 10/307]
Ref 2: Who was Ibn Abee Du’aad?
Shaikh Abdul Waahid Abu Khadeejah [may Allaah preserve him] quotes:
The author (Al-Barbahaaree) said: “Ibn Abee Du’aad  and Bishr al-Mireesee ..” These are the two that encouraged the ruler, Al-Ma’moon, to inflict punishment upon Imaam Ahmad (rahimahullaah) and upon others from the Scholars so as to extract from them the saying that the Qur’aan is created. Thumaamah Ibnul-Ashras  was from the leaders of the people of misguidance. Read here: https://www.abukhadeejah.com/imaam-barbahaaree-on-whoever-a-praises-an-innovator-allaamah-fawzaan-explains/