Umar bin Abdul-Aziz reported,

Rabi bin Sulayman al-Muadhdhin narrated to us, saying that Asad bin Musa narrated to us, saying that Hammad bin Dulayl narrated to us, saying, "I heard Sufyan Thawri narrate to us from Nadr." And Hannad bin al-Sari narrated to us from Qabisa, who said that Abu Raja narrated to us from Abu al-Salt. This is the wording of Ibn Kathir's narration, but the meaning of all of them is the same.He said, A man wrote to Umar bin Abdul-Aziz asking him about divine decree, and Umar wrote back:To proceed. I counsel you to fear Allah, to be moderate in carrying out His command, to follow the Sunnah of His Prophet ﷺ, and to abandon what innovators have introduced after his Sunnah was already established and its burden settled. Hold fast to the Sunnah, for by Allah's leave it will be your protection.Then know that people have never invented an innovation without there having already passed before it something that points to it or warns against it. The Sunnah was set down by one who knew full well what error lies in opposing it.(Ibn Kathir did not include the words "by one who knew.")Be content for yourself with what those people were content with for themselves, for they stopped at knowledge, and with penetrating insight they restrained themselves. They were stronger in uncovering matters and more deserving by virtue of what they possessed. If guidance is what you are upon, then you have outstripped them to it. And if you say that nothing was introduced after them except by one who followed a path other than theirs and turned away from them, well, they were the forerunners. They spoke about these matters with what suffices and described them with what heals. Whoever falls short of them has fallen short, and whoever goes beyond them has overreached. A people fell short of them and so were harsh, and others soared beyond them and so went to extremes. Yet they themselves stood between these two upon straight guidance.You wrote asking about affirming divine decree. By Allah's leave, you have written to one with knowledge of it. I know of nothing that people have introduced as a novelty, nor any innovation they have devised, whose trace is clearer or whose foundation is firmer than the affirmation of divine decree. It was spoken of even in the deepest age of ignorance. People mentioned it in their speech and their poetry, consoling themselves with it for what they had lost. Then Islam, when it came, only increased it in firmness.The Messenger of Allah ﷺ mentioned it in more than one or two hadiths. The Muslims heard it from him and spoke of it during his lifetime and after his death, with certainty and submission to their Lord, and acknowledging the weakness of themselves before the thought that anything could exist that His knowledge had not encompassed, that His Book had not enumerated, or that His decree had not already determined.Beyond all that, it is plainly stated in His decisive Book. From it they took it, and from it they learned it. If you say, "Why did Allah reveal such-and-such a verse?" or "Why did He say such-and-such?" they recited from it what you have recited and understood of its interpretation what you remain ignorant of. Then, after all that, they affirmed a Book and a decree, that wretchedness has been written, that whatever is decreed will come to pass, that whatever Allah wills happens and whatever He does not will does not happen, and that we possess for ourselves neither harm nor benefit. After affirming all this, they then engaged in hope and fear.

حدثنا محمد بن كثير قال حدثنا سفيان قال كتب رجل إلى

عمر بن عبد العزيز يسأله

عن القدر ح و حدثنا الربيع بن سليمان المؤذن قال حدثنا أسد بن موسى قال حدثنا حماد بن دليل قال سمعت سفيان الثوري يحدثنا عن النضر ح و حدثنا هناد بن السري عن قبيصة قال حدثنا أبو رجاء عن أبي الصلت وهذا لفظ حديث ابن كثير ومعناهم قال كتب رجل إلى عمر بن عبد العزيز يسأله عن القدر فكتب أما بعد أوصيك بتقوى الله والاقتصاد في أمره واتباع سنة نبيه ﷺ وترك ما أحدث المحدثون بعد ما جرت به سنته وكفوا مؤنته فعليك بلزوم السنة فإنها لك بإذن الله عصمة ثم اعلم أنه لم يبتدع الناس بدعة إلا قد مضى قبلها ما هو دليل عليها أو عبرة فيها فإن السنة إنما سنها من قد علم ما في خلافها ولم يقل ابن كثير من قد علم من الخطإ والزلل والحمق والتعمق فارض لنفسك ما رضي به القوم لأنفسهم فإنهم على علم وقفوا وببصر نافذ كفوا وهم على كشف الأمور كانوا أقوى وبفضل ما كانوا فيه أولى فإن كان الهدى ما أنتم عليه لقد سبقتموهم إليه ولئن قلتم إنما حدث بعدهم ما أحدثه إلا من اتبع غير سبيلهم ورغب بنفسه عنهم فإنهم هم السابقون فقد تكلموا فيه بما يكفي ووصفوا منه ما يشفي فما دونهم من مقصر وما فوقهم من محسر وقد قصر قوم دونهم فجفوا وطمح عنهم أقوام فغلوا وإنهم بين ذلك لعلى هدى مستقيم كتبت تسأل عن الإقرار بالقدر فعلى الخبير بإذن الله وقعت ما أعلم ما أحدث الناس من محدثة ولا ابتدعوا من بدعة هي أبين أثرا ولا أثبت أمرا من الإقرار بالقدر لقد كان ذكره في الجاهلية الجهلاء يتكلمون به في كلامهم وفي شعرهم يعزون به أنفسهم على ما فاتهم ثم لم يزده الإسلام بعد إلا شدة ولقد ذكره رسول الله ﷺ في غير حديث ولا حديثين وقد سمعه منه المسلمون فتكلموا به في حياته وبعد وفاته يقينا وتسليما لربهم وتضعيفا لأنفسهم أن يكون شيء لم يحط به علمه ولم يحصه كتابه ولم يمض فيه قدره وإنه مع ذلك لفي محكم كتابه منه اقتبسوه ومنه تعلموه ولئن قلتم لم أنزل الله آية كذا لم قال كذا لقد قرءوا منه ما قرأتم وعلموا من تأويله ما جهلتم وقالوا بعد ذلك كله بكتاب وقدر وكتبت الشقاوة وما يقدر يكن وما شاء الله كان وما لم يشأ لم يكن ولا نملك لأنفسنا ضرا ولا نفعا ثم رغبوا بعد ذلك ورهبوا