A well-known madrasa was built for him in Naysabur.
He passed away in Naysabur on the Day of ʿAshura in the year 418 AH.
Shaykh Abū Isḥāq said in al-Ṭabaqāt: “Our teacher Abū al-Ṭayyib studied under him, and most of the scholars of Naysabur derived their theology (kalām) and legal theory (uṣūl) from him” (1).
Another authority related: “His coffin was carried to Isfarayin, and he was buried there in his mausoleum” (2).
ʿAbd al-Ghafir said in his History: “Abū Isḥāq was the ornament of the entire eastern region—let alone of Naysabur. He was among those who strove hard in worship and were extreme in scrupulous piety. Al-Ḥākim selected ten fascicles from his narrations and mentioned him in his History because of his stature. The ḥadith master Aḥmad ibn ʿAlī al-Rāzī chose one thousand ḥadiths for him and convened a public dictation session. He was trustworthy and firmly established in ḥadith” (3).
Al-Ḥāfiẓ Ibn ʿAsākir said: “Someone I trust told me that the statesman Ismāʿīl ibn ʿAbbād, whenever he came to mention these men, would say:
‘Ibn al-Bāqillānī is a sea that engulfs,
Ibn Furak a viper that strikes,
and al-Isfarāyinī a fire that burns.’” (4)
Al-Ḥākim said in his History: “Abū Isḥāq, master of uṣūl, jurist and theologian, a pioneer in these sciences, returned from Iraq after the scholars there had acknowledged his precedence, to—”