It is whatever does not meet the conditions of tawātur.
Khabar al-wāḥid yields presumption (ẓann) in every case, although the grades of presumption vary.1
It has three sub-categories based on the number of narrators.2
This is the position of the majority. According to al-Samʿānī, al-Āmidī, Ibn al-Ṣalāḥ, Ibn Taymiyyah, al-Bulqīnī, Ibn Ḥajar, al-Suyūṭī and others, however, some solitary reports may yield theoretical (acquired) knowledge through supporting indications (qarāʾin). See: Qawāṭiʿ al-Adilla, 1/332 to 333; Muntahā al-Sūl, p. 79; Sharḥ Nukhbat al-Fikr, pp. 17 to 22; Tadrīb al-Rāwī, 1/131 to 134. ↩
Sharḥ Nukhbat al-Fikr, p. 15. ↩
Ḥadīth, in the muḥaddithūn's classification, is of two categories: al-mutawātir and khabar al-wāḥid.
Al-mutawātir is a ḥadīth narrated, on the basis of sensation rather than pure reason, by a number whose collusion upon falsehood is rendered impossible by ordinary custom.
The Ḥanafīs treat al-mashhūr as a third tier alongside al-mutawātir and khabar al-wāḥid, defined by what was āḥād in the first generation but tawātur thereafter.
When a single narrator takes a ḥadīth in solitary fashion from a prominent imām, it is called gharīb (literally, strange, or one who is alone).
