and Ahmad al-Wāsitī; al-Ḥasan ibn ʿAlī al-Iskāfī; al-Ḥasan ibn ʿAlī ibn Baḥr ibn Barri al-Qaṭṭān; al-Ḥusayn ibn Isḥāq al-Tustarī; and al-Ḥasan ibn Muḥammad ibn al-Ḥārith al-Sijistānī—al-Khallāl remarked, “His knowledge, acumen in hadith, and grasp of jurisprudence are almost on a par with Abū Dāwūd”—as well as Ismāʿīl ibn ʿUmar al-Sijzī, the ḥāfiẓ, and Aḥmad ibn al-Furāt al-Rāzī, the ḥāfiẓ, together with many others named by al-Khallāl among the followers of Abū ʿAbd Allāh. From them came transmissions of his legal questions in both large and small numbers.
Abū Bakr al-Khallāl then gathered everything those men possessed of Aḥmad’s statements, legal rulings, and remarks concerning hidden defects, narrators, the Sunnah, and subsidiary questions, until what he amassed became indescribably vast.
To obtain this material he journeyed through various regions, writing from nearly one hundred individuals who had been the Imam’s companions. He further collected a great deal from the companions of those companions, and some of it through a chain of one man from another, from yet another, back to Imam Aḥmad. After that he set about arranging, refining, and classifying it.
He produced Kitāb al-ʿIlm (The Book of Knowledge), Kitāb al-ʿIlal (The Book of Hadith Defects), and Kitāb al-Sunnah, each of the three in three volumes.
Along the way he also transmitted hadiths with lofty isnāds that he possessed from Aḥmad’s contemporaries among the pupils of Ibn ʿUyaynah, Wakīʿ, and the rest—evidence in itself of his leadership and pre-eminence.
He authored Kitāb al-Jāmiʿ in a dozen or more volumes.
In his work Akhlāq Aḥmad ibn Ḥanbal he declared, “I know of no one who has ever devoted himself to the questions of Abū ʿAbd Allāh as I have.”
Similarly, Abū Bakr al-Marūdhī (may Allah have mercy on him) used to say to me, “No one has cared for the questions of Abū ʿAbd Allāh as you have—save for a man in Hamdān named Mattawayh, whose full name is Muḥammad ibn Abī ʿAbd Allāh; he collected seventy large fascicles.”
Al-Khallāl was born during the lifetime of Imam Aḥmad, so it is possible that he saw him while still a child.