Why we need Fataawa
22-12-2005 | IslamWeb
Question:
What is a Fatwa? Can you please give me evidence from the Quran or Hadeeth of its existence? Why do we need Fataawa? Has Allaah not perfected our religion with the Quran and Hadeeth?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Fatwa means informing the questioner about the religious ruling on the question he is asking or the calamity or situation that befell him. Therefore, the Fatwa is based on the Book of Allaah, the Sunnah of His Prophet 
or consensus of the scholars
or analogy. For more benefit, please refer to Fatwa 89691.
Indeed there are many evidences from the Quran and the Sunnah of the Prophet about the permissibility of giving Fatwa [issuing religious rulings].
Evidences from the Quran:
Allaah Says (what means): {So ask the people of the message [i.e. former scriptures] if you do not know.}[Quran 21:7].
It is reported that Jaabir 
said: “A scholar should not conceal the knowledge that he has and an ignorant person should not keep quiet about his ignorance (i.e. he should ask about what he does not know), as Allaah Says (what means): {So ask the people of the message [i.e. former scriptures] if you do not know.}" [Ibn Mardawayh]. Indeed the Quran stated many questions which the companions 
used to ask the Prophet about. Allaah Says (what means): {They ask you for a legal ruling. Say, “Allah gives you a ruling concerning one having neither descendants nor ascendants [as heirs]”.}[Quran 4:176]. Allaah further Says (what means): {They ask your, [O Muhammad ], legal ruling concerning women. Say, “Allaah gives you a ruling about them…”}[Quran 4:127]. In another verse Allaah Says (what means): {They ask you about fighting in the sacred months (i.e. 1st, 7th, 11th and 12th months of the Islamic calendar).}[Quran 2:217]. Indeed there are many verses in this context but this is not the place.
Evidences from the Sunnah of the Prophet :
Um Saleem, 
came to the Prophet asking him about a legal ruling: "Does a woman have to perform Ghusl (ritual bath) if she sees a wet dream?" He replied: “Yes, if she sees any wetness [any wet discharges]." Moreover, ‘Ali asked the Prophet about the ruling of Mathiy [a clear pre-seminal discharge] and many companions asked him about many matters and their narrations are recorded in the books of Imaams Al-Bukhari and Muslim and many other books of Sunnah.
As regards your question: "Why do we need Fataawa [plural of Fatwa]?", the answer is that a person needs a Fatwa because he does not know the religious ruling; this does not mean that the legislation is not complete or that Allaah has not finalized his religion. Indeed many people, or say most of them, do not know by themselves the religious ruling that is in the Book of Allaah or the Sunnah of the Prophet so they have to ask the scholars in order to find out the religious ruling. Allaah Says (what means): {So ask the people of the message [i.e. former scriptures] if you do not know.}[Quran 21:7].
For instance if we ask you: “What is the waiting period of a divorced woman who reached the age of puberty but did not yet have menstruation?” You might not know the answer and you would not know it until you ask the scholars and then you will realize why you need a Fatwa.
Allaah Knows best.