Ahmad ibn Hanbal said:
Abd al-Rahmān narrated to us: Sufyān narrated to us, from Wāsil, from Mujāhid, who said:
“We used to relate that the devils were kept in chains during Umar’s rule. When Umar was killed, they sprang forth.”
This is an extensive subject on which scholars have written entire volumes concerning Umar’s virtues, such as the works of Abū al-Faraj ibn al-Jawzī and Umar ibn Shabbah(1), not to mention what Imam Ahmad ibn Hanbal and other leading scholars recorded, including Khaythama ibn Sulaymān’s Virtues of the Companions and the works of al-Dāraqutnī, al-Bayhaqī, and others.
[Umar’s Letter to Abū Mūsā al-Asharī Concerning Adjudication]
Umar’s renowned letter to Abū Mūsā al-Asharī concerning adjudication circulated among the jurists, who built upon it and relied upon the jurisprudence and principles of jurisprudence it contains. Among its chains of transmission is that related by Abū Ubayd, Ibn Battah, and others through an established chain from Kathīr ibn Hishām, from Jafar ibn Burqān, who said:(2)
Umar ibn al-Khattāb—may Allah be pleased with him—wrote to Abū Mūsā al-Asharī:
“Now then: adjudication is a firmly established obligation and a sunnah to be followed. Understand what is presented to you,(3) for merely pronouncing what is right(4) is of no avail without enforcement