`Aqaa’id refers to the aspects of knowledge and belief that are held, such as what relates to Tawheed, and the Names and Attributes of Allaah, and the affairs of the Unseen, such as Paradise, Hellfire, the Hawd, and the Angels, Jinn and so on. Manaahij, is a very broad term, and refers to the action based matters, and generally speaking it is used in relation to the affairs of da`wah, and rectification, and correction and cultivation and so on. When we say “manhaj” we actually mean what is found in the Sunnah in relation to what describes the precise way that one ought to behave or act, or proceed in a given situation.
To give some limited example of issues of “manhaj”:
1. how do you behave in the presence of tyrannical rulers?
2. how do you behave when people attack you in your home, such as the khawaarij or the bughaat? do you fight them, and then continue to chase after them and seek them out, or do you fight them only enough so as to repel them, and if they flee, then you leave them and refer the matter to the walee?
3. when you proceed upon calling people to Allaah, where do you begin?
4. how do you behave with the people of innovation?
5. how do you enjoin the good and forbid the evil?
6. were demonstrations and riots means of changing rulers and are they from the manhaj of the Salaf? No.
And so on.
All of these are affairs of manaahij, which are action-based, practical issues. And if you look in the books of the Salaf, you find that these matters are included as the USOOL, i.e. the foundations of the deen. So in these books you find that the Salaf speak about issues of aqeedah and they speak about issues of manhaj, and they do not differentiate between them, and they include all of them from the Usool, and they held that anyone opposing these affairs to be upon opposition and upon innovation. Also certain affairs of fiqh were included and were accepted as distinguishing features that separate between Ahl us-Sunnah and those who oppose them, such as wiping over the khuffayn.
Also manhaj can also refer to the approaches taken in deriving the understanding of the Book and the Sunnah.
For example, how do we understand the topic of Allaah’s Names and Attributes?
How do we extract rulings from the Book and the Sunnah? In each of these topics there are methodologies and courses of action. And again you find that the Salaf have included aspects of this in their books, such as accepting the authentic narrations concerning the Attributes and not rejecting them, and the censure of the use of intellect and opinion concerning the Sunnah (be that in relation to aspects of `aqeedah or fiqh) and so on.
The answer to your question is that even though the Salaf have not explicitly spoken of the link between `aqeedah and manhaj (and the falsehood of distinguishing between them) in the manner that the scholars quoted above have, then when you look at their books you find that this distinction was not present in their understanding. Rather to the Salaf, there were matters of Usool (foundations) and these foundations included` aqaa’id, and manaahij, and at times, limited issues of fiqh.
If you have a quick read through al-Barbahaaree’s book, you will see that this is clear inshaa’Allaah.
Shaykh Saalih al-Fawzaan – may Allaah preserve him – said, The reasons for disunity are many. From amongst the main causes are:
Firstly, opposing the manhaj (methodology) of the Salaf, the Companions of Allaah’s Messenger and those who follow them. So the Salaf had a manhaj that they adhered to; a manhaj in `aqeedah (creed), a manhaj in da`wah (calling to Allaah), a manhaj in enjoining good and forbidding evil, a manhaj in how to judge between people. This manhaj, in all situations, was based upon the Book of Allaah and the Sunnah of our Messenger . (Wujoob ut-Tathabbut fil-Akhbaaar p.18)
So in reality manhaj covers the course of action in all affairs of the religion, be that in `aqeedah or da`wah or fiqh, or tazkiyah etc. In our times, manhaj is referred more specifically to the issues in which controversy has entered into, like rebellions, takfeer of the rulers, jarh and ta`deel, co-operation with the Innovators, lenience towards them, jam`iyyaat and jamaa`aat, and all of these matters relate to the methodologies of da`wah that certain groups are upon, and in which they oppose the Salaf.