Hanbalee Usool
Understanding Islam
Bayaan at-Talbees Ahlul-Takfeer
Ahlu-Sunnah Versus the Ashari/Sufi Movement
The Senior Scholars Warn Against Extremism and Exageration in Religion
Muslim Authorities
Countering Islamaphobia
To Non Muslims
Salafi Conferences With Scholars
The four schools agree one the use of Qur'an, hadith, scholarly
consensus (ijma`), and analogical reasoning (qiyas). But even though
the schools agree on the use of these four sources, there are slight
differences in how each one is used. In addition, each school adds
additional sources to this list.

This leads to the obvious conclusion that differences the usul lead
to differences in the furu`.

It also leads to a less obvious conclusion that we cannot determine
which opinion is strongest until we have determined which usul is
strongest. This is not always a trivial task.

As for the usul of the Hanbali mathab, the basic list, since at
least the times of Ibn Qayyim Al-Jawziya, includes five:
1.      Al-Nass which includes the Qur'an and accounts from the
Prophet (Allah bless him and give him peace) that are rigorously- or
well- authenticated (respectively: sahih, hasn)
2.      A fatwa from one of the Companions when the other Companions
(Allah be well pleased with them one and all) are not known to
differ with it
3.      When there is a difference of opinion between the Companions
(Allah be well pleased with them one and all), then whichever one is
closest to the Qur'an and sunna; if it was not clear which opinion
was closest, then he would mention that there is a difference of
opinion without being convinced [of the superiority of any
particular one]
4.      Hadiths that are mursal, where one of the tabi`in (someone
who met at least one of the Companions (Allah be well pleased with
them)) ascribes a hadith to the Prophet without mentioning the
narrator(s) between himself and the Prophet (Allah bless him and
give him peace);
Hadiths which are weakly authenticated (da`if) when there is nothing
to refute it, however there is disagreement concerning the meaning
of "dha`if" here
5.      Analogical reasoning (qiyas)

But as Imam Muhammad Abu Zahrah points out in his book concerning
Imam Ahmad, the picture is a just bit more complicated than that. As
a minimum, we can add the following to the list:
6.      Al-Istishab, which is projecting a known ruling into the
past or present
7.      Al-Masalih Al-Mursala, which looking at the public interest
8.      Al-Thar`i, which is giving something the ruling of that
which is leads to