The ‘aqeedah has two fundamental sources, they are:-
 The Book of Allaah - the Most High (the Noble Qur’aan).
 What is authentic from Allaah’s Messenger (صلى الله علیه وسلم). Since the Messenger (صلى الله علیه وسلم) does not speak from desires, rather his words are Revelation sent down.
And the Ijmaa’ (consensus) of the Salafus-Saalih (Pious Predecessors): A source based upon the Book and the Sunnah. 
As regards the uncorrupted fitrah (natural state) and the sound and correct ’aql (intellect) then they will agree with and conform to the Book and the Sunnah and will be able to arrive at the general principles of ’aqeedah, but not its details. So the sound and correct ’aql and fitrah affirm Allaah’s existence and that He is Most Great and that it is essential to obey and to worship Him; and that He has the Attributes of Greatness and Majesty. Likewise, the sound ’aql and the uncorrupted fitrah realise the necessity of there being Prophets and the sending of Messengers; and that there has to be Resurrection and requital of actions; etc. - in general, but without the specifics and details.
However, as for other matters and the rest of the matters of the Ghayb (Unseen), then there is no way to find them out in detail, except by way of the Book and the Sunnah (the Revelation), otherwise it would not be from the Unseen. And contradiction between a clear text of the Book and the Sunnah and sound and correct ’aql cannot be imagined and is infact an impossibility. So if there appears to be a contradiction between the two then the Revelation is given precedence and is decisive  since it comes from the one who is infallible (صلى الله علیه وسلم), whereas the ’aql (intellect) of a person is not infallible. Indeed, the ’aql is the deficient perception of humans; and it is open to misconception, error, forgetfulness, desires, ignorance and inability - thus it is certainly deficient.
Its Principles and Methodology 
 The source for ’aqeedah is the Book of Allaah, the Sunnah of Allaah’s Messenger (صلى الله علیه وسلم) and the Ijmaa’ (consensus) of the Salaf (Pious Predecessors).
 Everything that we have with us authentically reported from Allaah’s Messenger (صلى الله علیه وسلم), then we have to accept it - whether it has been related in mutawaatir or aahaad form. 
 That which we refer back to in order to understand the Book and the Sunnah are those texts which explain others; and the understanding of the Salafus-Saalih (the Pious Predecessors)  and those Scholars who followed their manhaj (methodology); and then what is correct from the language point of view. However, we do not reject something established due to a possible language meaning.
 All the fundamental principles of the Deen were explained by the Prophet (صلى الله علیه وسلم). That which was not considered part of the Deen at that time cannot be considered to be part of the Deen later.
 Submission to Allaah and His Messenger (صلى الله علیه وسلم) both outwardly and inwardly. So we do not oppose anything from the Book, nor from the authentic Sunnah with qiyaas (analogy), personal views, kashf (intuition), nor the saying of any Shaykh or Imaam, etc.
 Correct and sound ’aql (reasoning or intellect) agrees with authentic naql (text) - these two conform - and what is qat’ee (definite) from either of them cannot contradict the other. If there is an apparent contradiction, then the text is given precedence.
 It is imperative and obligatory to adhere to the textual and Sharee’ah wordings in matters of ’aqeedah; and to avoid innovated terms and wordings. As regards wordings which contain more than one meaning and may be correct or incorrect, then the meaning should be ascertained; so if the meaning is correct then it is affirmed with a Sharee’ah wording. However, if the meaning is incorrect, then it is rejected.
 Infallibility (i.e. being ma’soom) is established for Allaah’s Messenger (صلى الله علیه وسلم). The Ummah as a whole is also maa’soom (infallible) and protected from uniting upon error and misguidance. However, as for the individuals of this Ummah, then they are not ma’soom (i.e. they err and make mistakes). So whenever there is a difference amongst the Scholars, then we refer it back to the Book and the Sunnah, along with making an excuse for the one who has erred and is mistaken; since he is from the mujtahidoon (those Scholars who are qualified to extract rulings from the Book and the Sunnah) of this Ummah.
 In this Ummah there are some who are muhaddath (addressed) with ilhaam (intuition). Good dreams are true and are a part of Prophethood. Likewise, truthful intuition is a true fact and is considered as being one of the karaamaat (miraculous occurrences) with the condition that it conforms to and agrees with the Revelation. However, such dreams and intuitions are neither a source for deriving matters of ’aqeedah nor Sharee’ah.
 Argumentation about the Deen is something censured, whilst debating in a good manner is something good and prescribed. However, there are certain matters which it is not permissible to debate and argue about. It is obligatory to withhold from speaking about those matters which one has no knowledge of and to refer knowledge of it back to Allaah.
 It is essential and obligatory to adhere to the same methodology of the Revelation when refuting. So an innovation is not refuted with another innovations, negligence and falling short is not refuted with extremity, nor is extremity refuted with negligence.
 Every newly-invented matter in the Deen is a bid’ah (innovation). Every bid’ah is a going astray and misguidance, and every misguidance is in the Fire.
 From Mubaahith fee ’Aqeedah Ahlus-Sunnah wal-Jamaa’ah (p.28).
 Refer to Al-I’tisaam (2/252) of ash-Shaadbee.
 Refer to Sharhul-’Aqeedatut-Tabaawiyyah (pp.140-141) of Ibn Abil-’Izz al-Hanafee. And refer also to Dar Ta’aarudil-’Aql ma’an-Naql (1/88-280) of Ibn Taymiyyah - and indeed, refer to the whole book as it is very beneficial in this matter.
 From Mujmal Usool Ahlus-Sunnah wal-Jamaa’ah fil-’Aqeedah (pp.7-9).
 See page 38; footnote numbers 3 & 4 for the definition of the terms mutawaatir and aahaad. Refer also to page 34 for a very brief discussion about this issue.
 From the clearest sign and greatest testimony of a person’s truly following the path of the Salafus-Saalih is clinging firmly to their sayings and their judgements with regards to ’aqeedah, which have been preserved in the earliest books of ’aqeedah and manhaj; and from these twelve principles have been derived. So from the earliest of these books are:-
- Kitaabul-Eemaan by the Imaam and mujtahid, Aboo ’Ubayd al-Qaasim ibn Salaam (d.224H).
- Kitaabul-Eemaan by Imaam Ibn Abee Shaybah (d.235H).
- Usoolus-Sunnah and Ar-Radd ’alal-Jahmiyyah waz-Zanaadaqah by the Imaam of Ahlus-Sunnah wal-Jamaa’ah Ahmad bin Hanbal (d.241H).
- Khalq Af’aalul-’Ibaad, Kitaabul-Eemaan and Kitaabut-Tawheed (the last two being part of al-Jaami’tis-Saheeh) by Imaam al-Bukhaaree (d.256H).
- As-Sunnah by the student of Imaam Ahmad, Aboo Bakr al-Athram (d.273H).
- Kitaabus-Sunnah (being part of the Sunan) by the faqeeh and Imaam, Aboo Daawood as-Sijistaanee (d.275H).
- Al-Ikhtilaaf fee Lafdh war-Radd ’alal-Jahmiyyah by Imaam Imaam Ibn Qutaybah (d.276H).
- Ar-Radd ’alal-Jahmiyyah by Imaam ad-Daarimee (d.280H).
- As-Sunnah by the qaadee and Haafidh, Ibn Abee ’Aasim (d.287H).
- As-Sunnah by the Haafidh, ’Abdullaah ibn Imaam Ahmad (d.290H).
- As-Sunnah by the qaadee and muhaddith Aboo Bakr al-Maroozee (d.292H).
- As-Sunnah by the student of Imaam Ahmad, al-Marwazee (d.294H).
- Sareehus-Sunnah by the mujtahid, mufassir and Imaam, Ibn Jareer at-Tabaree (d.310H).
- Kitaabut-Tawheed wa Ithbaat Sifaatur-Rabb by the faqeeh and Imaam, Ibn Khuzaymah (d.311H).
- ’Aqeedatut-Tahaawiyyah by the Imaam Aboo Ja’far at-Tahaawee (d.321H).
- Al-Maqaalaatul-Islaamiyyeen, Ar-Risaalah ilaa Ahlith-Thaghr and Al-Ibaanah ’an Usoolid-Diyaanah by Imaam Abool-Hasan al-Ash’aree (d.324H).
- Ahlus-Sunnah by the Haafidh and Imaam, Aboo Haatim ar-Raazee (d.327H).
- Sharhus-Sunnah by the Imaam of Ahlus-Sunnah wal-Jamaa’ah in his time, Imaam al-Barbahaaree (d.329H).
- Kitaabus-Sunnah by the qaadee, Aboo Ahmad al-’Asaai (d.349H).
- Ash-Sharee’ah by the faqeeh and Imaam, Aboo Bakr al-Aajurree (d.360H).
- I’tiqaad A‘immatul-Hadeeth by the faqeeh and Imaam, Aboo Bakr al-Ismaa’eelee (d.371H).
- Kitaabus-Sifaat and Kitaabun-Nufooz by the Haafidh, the Imaam, ad-Daaraqumee (d.385H).
- Al-Ibaanbah ’an Sharee’atil-Firqatin-Naajiyah and Sharhul-Ibaanah ’an Usoolis-Sunnah wad-Diyaanah by the Haafidh, the faqeeh, the Imaam, Ibn Battah al-Akbaree (d.387H).
- Kitaabut-Tawheed and ar-Radd ’alal- Jahmiyyah both by the Haafidh and Imaam, Ibn Mandah (d.395H).
- Sharh Usool I’tiqaad Ahlns-Sunnah wal-Jamaa’ah by the Haafidh and faqeeh, Imaam al-Laalikaa‘ee (d.418H).
- Al-Wusool ilaa Ma’rifatil-Usool by Imaam Aboo ’Amr at-Talamankee al-Andalusee (d.429H).
- Al-I’tiqaad by Aboo Nu’aym al-Asbahaanee (d.430H).
- Risaalah fee Ithbaatil-Istiwaa by Imaam Aboo Muhammad al-Juwaynee (d.438H).
- ’Aqeedatus-Salaf Ashaabul-Hadeeth by the Haafidh and Imaam, Aboo ’Uthmaan as-Saaboonee (d.449H).
- Al-I’tiqaad ’alaa Madhhabis-Salaf Ahlus-Sunnah wal-Jamaa’ah by Imaam al-Bayhaqee (d.457H).
- Dhammal-Kalaam by the Haafidh and faqeeh, Shaykhul-Islaam Aboo Ismaa’eel al-Harawee (d.481H).
So - O noble reader - beware of those who speak about this vital matter without reference to the above-mentioned sources and without following the understanding of the Salaf of this Ummah - since such people have innovated, deviated and have left the safe and well-trodden path - and only Allaah guides to the Path that is straight.