Bismillahi Al-Rahmani Al-Rahim
This opinion is mentioned as being from Imaam Ahmad in Uddah by baha
ud-din al-maqdisi and also in manar as-sabeel so it is definantly part of
the madhab. So if one were to follow it he would definantly be following
the madhab although it could be said that he would not be following the
strongest opinion in the madhab.
As for Ibn Taymiyah's opinion then from the perspective of proof it is
very strong since he brings the ahadeeth of tanning and the prohibition
from certain animals together. Also Ibn Taymiyah is viewed by many people
to have been a mujatahid so if one holds this opinion then it would be
perfectly fine to follow his opinion.
Wa `alaykum al-salam wa rahmatullahi wa barakatuhu
Yes, the position is mentioned in works like Al-`Uddah and Manar Al-Sabil,
and the evidence is strong; how could it be otherwise, when it is the basis
of the opinions of Imams Abu Hanifa, Abu Yusuf, and Imam Al-Shafi`i (Allah
be merciful with them all)? But the question remains: has this position
ever been given in a book of fiqh that was relied upon for fatwa? It
certainly was not the position given by Al-Khiraqi, Ibn Qudamma,
Al-Hajjawi, Al-Bahuti, or Mar`i Bin Yusuf (Allah be merciful with them
Imam Ahmad (Allah be merciful with him) often has multiple opinions on a
given issue. Whenever there is an explicit text that is strong enough to be
used for legal purposes, it is considered an opinion. Many of these
opinions, even some that have strong evidence, have never been used by
later scholars of the mathab.
So, as for this ruling here: a book like `Ali Mardawi's Al-Insaf Fi
Ma`rifati Al-Rajih Min Al-Khilaf should be consulted to see whether this
particular riwaya has ever been used as an opinion in the mathab.
This is why I am hesitant to agree to a statement that someone following
this opinion would "definately" be following the mathab.
As for Ibn Taymiyyah's opinion (Allah be merciful with him) and it being
very strong because he brought together the various hadiths dealing with
tanning: Ibn Qudamma and the others did the same, so by this metric it
means that their position is also very strong. But the subject here is the
mathab of Imam Ahmad, and it seems quite telling that the early, middle,
and late scholars of the mathab agree on a different position. Determining
the mathab's position on a given issue involves more than picking one of
Imam Ahmad's riwayat and then listing the hadiths that support it.
Just curious: What does Ibn Taymiyyah do with the account that the Prophet
(Allah bless him and give him peace) sent a letter two months before his
death, containing: "I used to give you a dispensation to use the skins of
dead animals. If this writing of mine reaches you: do not use the skins and
sinew of dead animals" [slight paraphrase]? This statement here is part of
the evidence used for the mufta bihi opinion, namely that it abrogates the
opinion that the tanning a dead animal will make it pure.
And as for following the ijtihad of Ibn Taymiyyah, if you heard it
directly from him or if the opinion reached you "bi tawattur" then it would
be possible to follow for personal practice but you could not use it for
fatwa. Fortunately, books like Ibn Mufluh's Al-Furu` have been read in each
successive generation to meet that condition. And Allah knows best.