As for a singular hadith, it is one known through only a single route of transmission. It may nevertheless be authentic, as with the hadith:

“Actions are only according to intentions”;

the report of “his prohibition of selling or giving away the right of patronage”; and the hadith that “he entered Mecca wearing a mail coif.”

These are authentic hadiths recorded by al-Bukhārī and Muslim, yet hadith scholars classify them as singular. The first is established only through Yahyā ibn Saʿīd al-Ansārī, from Muhammad ibn Ibrāhīm al-Taymī, from ʿAlqamah ibn Waqqās al-Laythī, from ʿUmar ibn al-Khattāb. The second is known only through the narration of ʿAbd Allāh ibn Dīnār from Ibn ʿUmar. The third is known only through Mālik’s narration from al-Zuhrī, from Anas. Most singular hadiths, however, are weak.

As for a fair hadith in al-Tirmidhī’s terminology, it is one transmitted through two routes, none of whose narrators is accused of lying, and which does not anomalously contradict authentic hadiths.

These are the conditions al-Tirmidhī stipulated for a fair hadith. Some, however, object that he has described hadiths as fair even though they do not meet these conditions. For example, he may describe a hadith as “fair and singular”: it has been transmitted through only one route, yet he has called it fair. The response given is that it may be singular because it has been transmitted from only one Successor, while being transmitted from that Successor through two routes. It thus becomes fair because of the multiple routes from that individual, although it is singular at its origin.

Likewise, a hadith may be described as “authentic, fair, and singular” because it has been transmitted through an authentic, singular chain, and then transmitted from the original narrator through one authentic route and another route