the Fatwa Department Research Committee - chaired by Sheikh `Abd al-Wahhâb al-Turayrî
Juristic consensus (ijmâ’) is the agreement of all of the people of knowledge of a given generation (whether it is the generation of the Companions or any generation thereafter) on a matter of Islamic Law.
When this consensus occurs, it indicates to us that there can be no doubt about the ruling that was arrived at., since the Prophet (peace be upon him) has informed us that his Ummah would never agree on a falsehood.
This is important, since many questions of Islamic Law are open to disagreement and multiple points of view. However, in matters of juristic consensus, no Muslims are allowed to disagree.
Juristic consensus is not contrary to any text. Actually, we must know that it is based in some text or another, even if the hadîth it is based on has not reached us. The reason for this is that the Prophet (peace be upon him) informed us that his Ummah would never agreed on an error, and having an opinion contrary to the Qur’ân and Sunnah is as blatant an error as there can be.
There is consensus on a number of issues. For instance, there is consensus that the five pillars of Islam are obligatory upon the Muslims, that a grandmother has a 1/6 share of the inheritance, that it is prohibited for a man to be married to a woman and her aunt at the same time, and that sujûd al-tilâwah can be performed without wudû’.
Source: Islam Today