Praise be to Allaah.
Allaah, may He be exalted, says (interpretation of the meanings):
The command (or the judgement) is for none but Allaah. He has commanded that you worship none but Him [Yoosuf 12:40]
And say not concerning that which your tongues put forth falsely: This is lawful and this is forbidden., so as to invent lies against Allaah. Verily, those who invent lies against Allaah will never prosper. [al-Nahl 16:116]
Say [O Muhammad, to the polytheists]: Tell me, what provision Allaah has sent down to you! And you have made of it lawful and unlawful. Say [O Muhammad]: Has Allaah permitted you (to do so) or do you invent a lie against Allaah? [Yoonus 10:59]
It is only for Allaah to say what is halaal and what is haraam, because He is the Law-giver, and there is no law-giver besides Him. When we say that a given thing is haraam, or halaal, we refer to the evidence in the Book of Allaah and the Sunnah of His Messenger (peace and blessings of Allaah be upon him). Whatever we find is prohibited therein, we take as haraam, and whatever we find is permitted, we take as halaal. We refer to the sayings of the Sahaabah (Companions of the Prophet (peace and blessings of Allaah be upon him) and the Taabieen (the generation after the Sahaabah) may Allaah be pleased with them and the commentaries of the Salaf (first generations of Islam) on the texts of the Quraan and Sunnah, and we refer to the sayings and ijtihaad of the scholars.
It is not permissible for us to allow or prohibit however we wish. When new issues come up, if we do not find a text in the Quraan or Sunnah, or in the sayings of the scholars of the salaf or the scholars of Ahl al-Sunnah wal-Jamaaah who came before us, then we have to refer to trustworthy scholars and people of understanding, as Allaah commands us (interpretation of the meaning): so ask of those who know the Scripture [al-Nahl 16:43]. These are the scholars, who can do ijtihaad, examine the matter and make analogies (qiyaas) with the existing texts of Islam, taking into consideration the principles of necessity, and taking note of what is harmful to the interests of shareeah and what is beneficial, relying on the basic general principles of shareeah, such as the aayah (interpretation of the meaning), he allows them as lawful al-tayyibaat [(i.e., all good and lawful things as regards things, deeds, beliefs, persons, foods, etc.] [al-Araaf 7:157] and the hadeeth, There should be no harming nor reciprocating harm(reported by Ibn Maajah, 2331), and avoiding following whims and desires. Every evil thing that is proven to be harmful is haraam, and every good and beneficial thing is halaal. If it is not known that it is either harmful or beneficial, then the general rule is that it is permissible (mubaah). And Allaah knows best.