Why Hadîth Was Not Generally Written
It is, however, a fact that the sayings of the Prophet were not generally written, and memory was the chief means of their preservation.
The Prophet sometimes objected to the writing down of hadîth. But this disapproval clearly shows nothing else but fear lest hadîth be mixed up with the Glorious Qu’ran. There was nothing essentially wrong in writing down hadîth, nor did the Prophet ever forbid its being done. Nor was memory an unreliable means for the preservation of hadîth, for the Glorious Qu’ran itself was safely preserved in the memory of the disciples of the Prophet in addition to committing it to writing. In fact, had the Qu’ran been simply preserved in writing, it could not have been handed down intact to future generations. The aid of memory was invoked to make the purity of the text of the Qu’ran doubly sure.
The Arab had a wonderfully retentive memory and he had to store knowledge of countless things in his memory. Indeed, before Islam, writing was but rarely resorted to, and memory was chiefly relied upon in all important matters. Hundreds and even thousands of verses could be recited from memory by one man, and the reciters would also remember the names of the poets through whom these verses had been transmitted to them. It is recorded of a later renowned transmitter, Asma’i by name, that he learned twelve thousand verses by heart before he reached majority. Another transmitter was reported to have recited verses from a hundred poets in a single sitting. Sha’bi, a famous transmitter, proved that he could continue reciting verses which he knew by heart for a month; and these verses were the basis of the Arabic vocabulary and even of Arabic grammar.
The Qu’ran Is the Greatest Test for Judging Hadîth
In addition to the above rules of criticism, which left little to be desired, there is another very important test whereby trustworthiness of Hadîth may be judged, and it is a test that the application whereof was commanded by the Prophet himself.
As already stated, hadîth is but an explanation of the Qu’ran; and hence also the Qu’ran must have precedence over the hadîth. It is unquestionable that the Qu’ran had been handed down intact every word and every letter of it, while hadîth could not claim that purity, and it was chiefly the substance of sayings that was reported. Again the Qu’ran deals with the principles of the Islamic Law while hadîth deals with the details, so that only such details should be accepted as are in accordance with the principles.
The Sunni Muslim community are agreed on the principle that a hadîth may be unacceptable either on account of there being some defect in its transmitters or because its subject-matter is unacceptable. Thus, all trustworthy collectors of traditions of the Prophet are at one that among the most important reasons for which a hadîth may be rejected is its subject-matter. For instance, if a reported tradition contradicts the Glorious Qu’ran or the recognized Sunnah or the unanimous verdict of the Muslim community, it is not accepted.
The following saying of the Prophet will explain the position, which he intended to assign to the oral law of hadîth or Sunnah:
“I do not make a legal thing illegal, nor do I make an illegal thing legal, but by Allâh.” [Sahih Al-Bukhari, Volume 4, Book 53, 342]
“Verily the best word is the word of God, and the best guidance of life is that delivered by His Prophet Mohammad.” [Dictionary of Islam p. 369], “I have left you two things and you will not stray as long as you hold them fast. The one is the Book of God and the other the Law (Sunnah) of his Prophet. ” [Mishkat 1:120, Volume 1, p 173]
The “Six Correct” Hadîth Books
There is some difference of opinion as to who first attempted to collect the traditions, and to compile them in a book. Some scholars say “Abdul-Malik ibn Juraij of Makkah, who died in 150 A.H., whilst others assert that the collection, which is still extant by the Imâm Mâlik ibn Anas, who died in 179 A.H., was the first collection. The work of the latter is still held in very great esteem, although it is not generally included among the standard Six Sihaah books, i.e. the “six correct” books received unanimously by Sunni Muslims. In a previous passage of this work the names of these six books were given; once more they are the collection of:
1) Al-Imâm Muhammad ibn Ismâ’il Al-Bukhâri, 256 A.H.
2) Al-Imâm Muslim ibn Al-Hâjjâj, 261 A.H.
3) Al-Imâm Abû-Dâwûd Solimân, 275 A.H.
4) Al-Imâm Muhammad ibn Isa Al-Tirmizi, 279 A.H.
5) Al-Imâm Ibn Mâja, abû-‘Abdullâh Muhammad, 283 A.H.
6) Al-Imâm An-Nasâ’i, Abû-‘Abdul-Rahmân, 303 A.H.
Besides these, the collections of Imâm Al-Shâf’i [204 A.H.], Ibn Idris, Imâm Ahmed ibn Hanbal [241 A.H.], Imâm Mâlik ibn Anas [179 A.H.], are also considered authentic by Sunni Muslims. 
 It was in this safe custody [memory] that the beautiful poetry of the pre-Islamic days had been kept alive and intact.
 Vide “An Essay on Muhammadan Tradition”, by the honourable Syed Ahmad Khan of Bahasour. Cf. “Nukhbatul-Fakr”, by Sheikh Shahab-ed-Din Ahmad.
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