It was mentioned in the first section authentic Hadiths that are agreed upon. As for the controversial type, it is included in this type according to those who disagree about its authenticity.
Unfamiliar Hadith has other types according to multiple ways.
A Hadith may be reported in authentic books of Hadith but unfamiliar from its way of narration such as the Hadith of Jabir ibn `Abdullah about digging the ditch, the Prophet's hunger, tying his stomach, and mentioning the description of the people of As-Suffah (Poor Immigrants who used to live in a covered section of the Prophet's Mosque). It is a long Hadith which Al Bukhari reported from the way of `Abdul-Wahid ibn Ayman on the authority of his father, and it is one of the unfamiliar authentic Hadiths.
Another example is the Hadith of `Abdullah ibn `Amr when the Prophet besieged At-Ta'if and his saying: "We will return (to Medina) if Allah wills." It was reported by Imam Muslim in his book and it is unfamiliar from the narration of As-Sa'ib ibn Farrukh, the poet, on the authority Ibn`Amr.
And from the unfamiliar types of Hadiths are unfamiliar Hadiths reported by sheikhs such as the saying of Ibn `Umar that the Prophet (peace be upon him) said: "A town dweller should not sell the goods of a desert dweller on behalf of the latter." Reported by Ar-Rabi` ibn Sulayman from Al Shafi`y from Malik from Nafi` on the authority of Ibn `Umar, however none reported the Hadith from Malik but Al Shafi`y and none had reported the Hadith from Al Shafi`y but Ar-Rabi`.
And from the unfamiliar types of Hadiths also are unfamiliar texts as Muhammad ibn Al Munkadir reported on the authority of Jabir that the Messenger of Allah (peace be upon him) said: "Indeed, this religion is firm, so, treat with it gently." The text of this Hadith is unfamiliar and its chain of transmission is unfamiliar too.
Al Ifrad, which means that the people of a town narrate some Hadiths from a certain Companion from the Prophet (peace be upon him) without sharing these Hadiths with another town or a single narrator narrates some Hadiths from a famous Imam without sharing it with other narrators such as the Hadith of Hammad ibn Salamah from Abu Al `Ushara' on the authority of his father who said: I said: O Messenger of Allah, is the slaughtering only from the throat and upper part of the breast? He said: If you strike the spear in its thigh, it is enough." This Hadith was reported only by Hammad ibn Salamah from Abu Al `Ushara' and there is no other Hadith was known from Abu Al `Ushara' but this one. However, the Hadith was well-known to the people of knowledge from the narration of Hammad.
Perhaps a Hadith that is reported by an Imam becomes famous for the multiple narrators who report it from him such as the Hadith of `Abdullah ibn Dinar on the authority of Ibn `Umar that the Prophet (peace be upon him) disallowed the selling of guardianship, or giving it as a gift. This Hadith was not known except from the Hadith of `Abdullah ibn Dinar from `Ubaydullah ibn `Abdullah ibn `Umar, Shu`bah, Sufyan Ath-Thawry Malik ibn Anas, and other Imams.
A Hadith may become unfamiliar because of an addition in its text. It will become authentic if the addition was reported by a trustworthy narrator such as the Hadith reported by Malik ibn Anas from Nafi` on the authority of Ibn `Umar who said: "The Messenger of Allah (peace be upon him) ordained the Zakah of breaking the fast in Ramadan on every free and slave, male and female Muslims: One Sa` of fresh dates or one Sa` of barely." However, Malik added in this Hadith the word "Muslims." Abu Ayyub As-Sikhtiyany, `Ubaydullah ibn `Umar, and others reported this Hadith from Nafi` on the authority of Ibn `Umar without mentioning the word "Muslims."
Some scholars approved the addition of Imam Malik and hold it as a proof such as Al Shafi`y, Ahmad ibn Hanbal, and others.
They said: If a person has non-Muslim slaves, he should not pay Zakatul-Fitr on their behalf.
So, if a trustworthy narrator adds something, it will be accepted from him but the Hadith will be considered unfamiliar because of this addition.
Some Hadiths may be famous, known to people, and circulated among scholars but they were not reported in books of authentic Hadiths.
On the other hand, some Hadiths may be reported in the books of authentic Hadiths but they are not famous and not circulated among people.
There may be some Shadh (a Hadith narrated by a trustworthy narrator, not in line with the narration of other trustworthy narrators in terms of wording, chain of narrators, or both) nevertheless it has no origin or similar Hadiths, so the Shadh disagrees with other narrations without having a cause for the Hadith to be narrated in this way. The problem of Hadith Mu`allal (any Hadith that has a hidden and ambiguously defective element while it apparently seems defectless by meeting all acceptability conditions.) is removed by knowing the causes of defects. However, the cause of Shadh Hadith is not known.
There may be a Hadith reported from many ways but its chain of transmission is unfamiliar such as the Hadith of Abu Kurayb, Abu Hisham Ar-Rifa`y, Abu As-Sa'ib, and Al Husayn ibn Al Aswad who said: Abu Usamah told us from Burayd ibn `Abdullah ibn Abu Burdah from his grandfather Abu Burdah on the authority of Abu Musa that the Prophet (peace be upon him) said: "A disbeliever eats in seven intestines (eats much food) but a believer eats in one intestine (is satisfied with a little food)." This Hadith is Gharib (a Hadith with a single narrator usually at the beginning of the chain of narration) in regard to its chain of transmission because this Hadith was reported from other ways but it is unfamiliar from the way of Abu Musa.
At-Tirmidhy said: Hadiths which we mentioned in our book "Al Jami`" "are good" and the meaning is good according to our conditions which are: Each Hadith should not have in its chain of transmission a narrator who is accused of lying, a Hadith is not Shadh and is reported from different ways; such Hadiths are good.
So, a good Hadith is a class between an authentic and unfamiliar Hadiths.
And Allah knows best!
These are the last words in the third chapter of this introduction.