Regarding following the madhaahib:
And in the furoo' (branches) of the religion we are upon the madhhab of Imaam Ahmad ibn Hanbal, and we do not object to whoever follows one of the four imaams, as opposed to other than them whose madhaahib have not been clarified.
The Raafidhah, Zaydiyyah, Imaamiyyah and the likes of them: we do not accept from them anything from their corrupt madhaahib, rather we require that they follow one of the four imaams.
And we do not deserve the level of al-ijtihaad al-mutlaq (absolute ijtihaad), and none among us claims it. However, in some matters, if we find an authentic nass (text) from the Book or the Sunnah that is not abrogated or specified or contradicted by a stronger evidence, and one of the four imaams says according to it, then we take it and leave the saying of the madhhab, such as the matter of the inheritance of the grandfather and the brothers, for we put the grandfather first in the inheritance, even though the madhhab of the Hanaabilah says otherwise.
And we do not inquire into a person's madhhab, and we do not oppose him, unless we find a clear text opposing the madhhab of one of the imaams in a matter involving an outward symbol of the religion (shi'aar), such as the imaam of the prayers; so we order the Hanafi and the Maaliki, for example, to observe the same calmness when rising from rukoo' (i'tidaal), and in the sitting between the sajdatayn, due to the clear evidence for that, as opposed to the Shaafi'i imam reciting the basmalah aloud, for we do not order him to recite it quietly. And there is a great difference between these two matters. So when the evidence is strong, then we advise them to follow the nass, even if it opposes the madhhab, and that is found only very rarely.
And there is no objection to ijtihaad in some matters as opposed to others, and this is not contradictory to the lack of the claim to ijtihaad. For it has been that a group of the imaams of the four madhaahib had their own particular views regarding certain matters that were in opposition to their madhhab, whose founder they followed.