(ii) The _Sahih_ of Muslim (817-875) with an introduction on the science of tradition (ed. Calcutta, 1849, &c.). (iii) The _Kitab us-Sunan_ of Abu Da`ud (817-888) (ed. Cairo, 1863, Lucknow, 1888, Delhi, 1890). (iv) The _Jami` us-Sahih_ of Tirmidhi (q.v.). (v) _The Kitab us-Sunan_ of Nasa` i (830-915) (ed. Cairo, 1894). (vi) The _Kitab us-Sunan_ of Ibn Maja (824-866) (ed. Delhi, 1865 and 1889). The last four are not held in the same repute as the first two. 3. _Ijma`_ is the universal consent which is held to justify practices or beliefs, although they are not warranted by the Koran or tradition, and may be inconsistent with the apparent teaching of one or both of these. These beliefs and practices, which had often come from the pre-Islamic customs of those who had become believers, seem to have escaped notice until the Abbasid period. They were too deeply rooted in the lives of men to be abolished. It became necessary either to find a tradition to abrogate the earlier forbidding one, or to acknowledge that _ijma`_ is higher than the tradition. The former expedient was resorted to by some later theologians (e.g. Nawawi) by a fiction that such a tradition existed though it was not found now in writing. But in earlier times some (as Ibn Qutaiba) had adopted the latter alternative, saying that the truth can be derived much earlier from the _ijma`_ than from the tradition, because it is not open to the same chances of corruption in its transmission as the latter. Tradition itself was found to confirm this view, for the Prophet is related to have said, "My people does not agree to an error." But _ijma`_ itself has been used in different senses: (i) The _ijma`_ of Medina was used to indicate the authority coming from the practices of the people of Medina (see below). (ii) The _ijma`_ of the whole community of Moslems is that most commonly recognized. It was used to support fealty to the Abbasid dynasty. By it the six books of tradition mentioned above are recognized as authoritative, and it is the justification of the conception of Mahomet as superhuman. (iii) Some of the more thoughtful theologians recognize only the _ijma`_ of the doctors or the teachers of Islam (the _mujtahidun_), these being restricted by the orthodox to the first few generations after Mahomet, while the Shi`ites allow the existence of such up to the present time. 4. The fourth basis of Islam is _qiyas_, i.e. analogy. It is that process by which a belief or practice is justified on the ground of something similar but not identical in the Koran, the tradition or _ijma`_. Originally it seems to have been instituted as a check upon the use of private opinion (_ra'y_) in the teaching of doctrine. The extent to which it may be used is a subject of much discussion among theologians. Some would apply it only to a "material similarity," others to similarity of motive or cause as well.