Is following the four madhhabs included in the hadeeth about the 73 sects?

Praise
be to Allah.

The well known
hadeeth about the ummah splitting into seventy-three sects is the hadeeth
of Mu‘aawiyah ibn Abi Sufyaan (may Allah be pleased with him), who said:
The Messenger of Allah (blessings and peace of Allah be upon him) stood up
amongst us and said: “Those who came before you of the people of the Book
split into seventy-two sects, and this ummah will split into seventy-three
sects, seventy-two of which will be in the Fire and one in Paradise. That
is the jamaa’ah (the main body of Muslims).”

Narrated by Abu
Dawood (4597) and others; classed as saheeh by al-Haakim (1/128). In fact he
said: It is an important hadeeth that highlights a major fundamental issue.
It was also classed as saheeh by Ibn Taymiyah in Majmoo‘ al-Fataawa
(3/345), ash-Shaatibi in al-I‘tisaam (1/430) and al-‘Iraqi in
Takhreej al-Ihya’ (3/199). 

The hadeeth was
also narrated by at-Tirmidhi (2641) as follows: “My ummah will split into
seventy-three sects, all of whom will be in the Fire except one sect.” They
said: Who are they, O Messenger of Allah? He said: “[Those who follow] the
path which I and my companions follow.” It was classed as hasan by Ibn
al-‘Arabi in Ahkaam al-Qur’an (3/432), al-‘Iraqi in Takhreej
al-Ihya’ (3/284) and al-Albaani in Saheeh at-Tirmidhi. 

The words of the
Prophet (blessings and peace of Allah be upon him), “My ummah will split
into seventy-three sects” indicate that the differences that lead to
splitting are differences concerning fundamentals and beliefs, not in minor
issues and rulings of fiqh. 

The words of the
Prophet (blessings and peace of Allah be upon him) concerning the saved
group, “That is the jamaa‘ah (the main body of Muslims)” or, according to
another report “[Those who follow] the path which I and my companions
follow” also confirm that. Those who differ concerning minor issues are not
regarded as going beyond the bounds of the jamaa‘ah by doing so, or as going
beyond the bounds of the teachings of the Prophet (blessings and peace of
Allah be upon him) and his Companions. The Sahaabah differed concerning
various minor issues, but that did not lead to their splitting and becoming
divided. No one said that as a result of those (minor) differences they were
included in the hadeeth about the sects; rather they were one group
(jamaa‘ah), following one path and the same fundamentals of belief. The same
may be said about the four Imams, the founders of the madhhabs that are
followed, and other people of knowledge and virtue. They are the jamaa‘ah,
the saved group, Ahl as-Sunnah. Whoever deviates from their basic principles
and beliefs is the one who deserves to be included among the people of the
sects and innovators who go astray. 

Hence ash-Shaatibi
(may Allah have mercy on him) said: These sects only became sects because of
their differing from the saved group with regard to some fundamental matter
of religion, or one of the basic principles of sharee‘ah, not with regard to
a minor matter, because having a different view or an odd view on a minor
matter does not lead to a difference that would result in splitting and
division. Rather division occurs when there are differences concerning
fundamental matters.

End quote from
al-I‘tisaam (2/200) 

Thus it is known
that the four imams are innocent of division, as are their followers who
adhere to the basic principles of Ahl as-Sunnah. As for those who differ
from that and follow the ways of the Mu‘tazilah, Shi‘ah, Murji’ah or other
sects and followers of whims and desires, this is the one who has gone
against Ahl as-Sunnah and is included among the blameworthy sects. 

For more
information, please see the answer to question no. 90112 

And Allah knows
best.