Conditions for Acting upon Khabar al-Āḥād

Imam al-Manṣūr Billāh ʿAbdullāh ibn Ḥamzah (d. 614 AH) states in Ṣafwat al-Ikhtiyār fī Uṣūl al-Fiqh that his teacher, Shaykh Abū ʿAlī al-Ḥasan ibn Muḥammad ibn al-Ḥasan ibn Muḥammad al-Raṣṣāṣ (d. 584 AH), held that khabar al-āḥād is not acted upon in isolation. Rather, it is only accepted when supported by corroborating factors, such as that some of the Companions acted upon it (ʿamal baʿḍ al-ṣaḥābah), widespread circulation without rejection (al-intishār wa-ghayr al-inkār), confirmation by analogy (qiyās), or an apparent and established proof (dhāhirun maʿlūmun).

Source

Ṣafwat al-Ikhtiyār fī Uṣūl al-Fiqh, p. 183 By Imam al-Manṣūr Billāh ʿAbdullāh ibn Ḥamzah (d. 614 AH).