If you ask what is the best method of tafsir, the answer is that the best way is to explain the Qur'an through the Qur'an. For, what the Qur'an alludes to at one place is explained at the other, and what it says in brief on one occasion is elaborated upon at the other. But if this does not help you, you should turn to the Sunnah, because the Sunnah explains and elucidates the Qur'an. Imam Abu 'Abdullah Muhammad ibn Idris ash-Shafi'i has said: "All that the Prophet, peace be upon him, has said is what he has derived from the Qur'an." Allah has said:
"We have sent down to you the book in truth that you may judge between me, as Allah guides you; so do not be an advocate for those who betray their trust." [Al-Qur'an 4:105]
"We have sent down to you the message that you may explain clearly to people what has been sent to them, and that they think over it." [Al-Qur'an 16:44]
"We sent down the Book to you for the express purpose that you should make clear to them those things in which they differ, and that it should be a guide and a mercy to those who believe." [Al-Qur'an 16:64]
This is why the Prophet sallallahu 'alayhi wa sallam said:
"Know that I have been given the Qur'an and something like it." [Ahmad, Musnad, vol. IV 131; Abu Dawud, Sunan, Sunnah, 5]
Namely the Sunnah. In fact, the Sunnah, too has been given to him through wahy as the Qur'an, except that it has not been recited to him as the Qur'an. Imam ash-Shafi'i and other scholars have advanced a number of arguments in support of this point; but this is not the place to quote them. [For discussion see ash-Shafi'i, ar-Risalah]
In order to understand the Qur'an, you should first look to the Qur'an itself. If that does not help, then turn to the Sunnah.
The Prophet sallallahu 'alayhi wa sallam sent Mu'adh radiallahu 'anhu to Yemen and asked him: "How will you judge the cases (that come to you)?" He replied: "I will judge according to the Book of Allah." "But if you do not get anything there, what will you do?", the Prophet sallallahu 'alayhi wa sallam asked. He said: "I will refer to the Sunnah of the Prophet sallallahu 'alayhi wa sallam." "But if you do not get it even there, what will you do?", the Prophet sallallahu 'alayhi wa sallam asked again. He replied: "I will exercise my judgment." Hearing this the Prophet sallallahu 'alayhi wa sallam patted Mu'adh radiallahu 'anhu on the shoulder and said: "Praise be to Allah who has guided the Messenger of His Messenger to what pleases His Messenger."
This hadith has been reported in the Musnad and Sunan collections of hadith with a good isnad. [Ahmad, Musnad V:230, 236, 242; ad-Darimi, Sunan, Muqaddimah, 30; at-Tirmidhi, Sunan, Ahkam, 3; Abu Dawud, Sunan, Adhiyah, 11]
When you do not get any help from the Qur'an or the Sunnah, turn to the words of the companions. For they know the Qur'an better: they have witnessed its revelation, and passed through the situations in which it was revealed: and know it and understand it fully. This is particularly true of the scholars and leaders such as the four righteous caliphs and 'Abdullah ibn Mas'ud. Imam Abu Ja'far Muhammad ibn Jarir at-Tabari reports: Abu Kurayb narrated to us, saying: Jabir ibn Nuh informed us that: al-A'mash informed us from Abu Duha: from Masruq that 'Abdullah ibn Mas'ud said: "By the one besides whom there none having the right to be worshipped, there is no verse in the Qur'an about which I do not know in whose case and at what place was it revealed. If I were aware that anyone knew the Qur'an more than me, and I could reach him, I would certainly have gone to see him." [Ibn al-Athir, Jami' al-Usul fi Ahadith ar-Rasul, 1392/1972, vol. IX p. 48] Al-A'mash has also reported through Abu Wa'il that Ibn Mas'ud said: "When anyone of us learned ten verses of the Qur'an, he did not proceed further unless he had known what they meant and what action they demanded."
Another great scholar is 'Abdullah ibn 'Abbas radiallahu 'anhuma, the nephew of the Prophet sallallahu 'alayhi wa sallam and the commentator of the Qur'an. He attained that stature in virtue of the Prophet's prayer: "O Allah! Give him knowledge of Islam and teach him the meaning of the Qur'an" [Ahmad, Musnad, vol. 1: 266, 314, 328, 335]. Muhammad ibn Bashshar narrated to us, that Waki' informed us, that Sufyan informed us from al-A'mash: from Musim (ibn Sabih Abi Duha) from Masruq: that 'Abdullah ibn Mas'ud radiallahu 'anhuma said: "What a good interpreter of the Qur'an Ibn 'Abbas is!" Ibn Jarir has also reported this hadith through Yahya ibn Dawud, from Ishaq al-Azraq, from Sufyan, from al-A'mash, from Muslim ibn Sabih Abi Duha, from al-Masruq with slightly different words: "What a good interpreter Ibn 'Abbas is of the Qur'an!" He has also reported the same words through Bundar, from Ja'far ibn 'Awn from al-A'mash. These words are, therefore, the actual words of Ibn Mas'ud radiallahu 'anhuma which he said about Ibn 'Abbas radiallahu 'anhuma. Ibn Mas'ud radiallahu 'anhuma died, most probably, in 33H. Ibn 'Abbas radiallahu 'anhuma lived for thirty six years after him, and added a lot to the treasury of Islamic knowledge.
Al-A'mash quotes from Abu Wa'il that Ibn 'Abbas radiallahu 'anhuma was appointed leader of the Hajj by 'Ali radiallahu 'anhu; he delivered a sermon and read from Surah al-Baqarah, or Surah an-Nur according to another report, and explained it in such a way that had the Romans, Turks and the Dalamites heard it, they would have embraced Islam. This is the reason why most of what Isma'il ibn 'Abdur-Rahman Suddi has written in tafsir consists of the explanations of these two scholars: Ibn Mas'ud and Ibn 'Abbas radiallahu 'anhum.
(s) An Introduction to the Principles of Tafsir
(p) Al-Hidaayah Publishing and Distribution