Ibn al-Salah said,"A hadith, according to its specialists, is divided into ṣaḥīḥ("authentic"), Ḥasan and ḍaʻīf.
Ibn al-Salah said:"A hadith, according to its specialists, is divided into ṣaḥīḥ, Ḥasan and ḍaʻīf.
Abū‘ Alī al- Ḥasan ibn al-
Haytham( Alhazen) of Basra( 10th- 11th century), mathematician and physicist; made significant contributions to the theory of optics, including refraction, reflection, binocular vision, and atmospheric refraction; first to explain correctly vision as the effect of light coming from an object to the eye.
Ibn Hajar defines a hadith that is Ḥasan lithatihi-"Ḥasan in and of itself"- with the same definition a ṣaḥīḥ hadith except that the competence of one of its narrators is less than complete;
while a hadith that is Ḥasan ligharihi("Ḥasan due to external factors")
is determined to be Ḥasan due to corroborating factors such as numerous chains of narration.