How the Quran and the Sunnah can be as the source of knowledge in economics?

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.

First of all, the Quran is a book of guidance for mankind as it guides them to the good of this world and the Hellfire. Allaah Says (what means): {Indeed, this Quran guides to that which is most suitable.}[Quran 17:9]. Therefore, it is a life guideline and methodology. The Quran solved some problems which hinder the economy. For instance, it forbade Ribaa (interest or usury); Allaah Says (what means): {But Allah has permitted trade and has forbidden interest.}[Quran 2:275]. Allaah also prohibited giving insufficient or deficient measures of weight (i.e. cheating). Allaah Says (what means): {Give full measure and do not be of those who cause loss. And weigh with an even [i.e. honest] balance. And do not deprive people of their due and do not commit abuse on earth, spreading corruption.}[Quran 26:181-183]. Besides, Allaah prohibited eating people’s money without right. Allaah Says (what means): {And do not consume one another’s wealth unjustly or send it [in bribery] to the rulers in order that [they might aid] you [to] consume a portion of the wealth of the people in sin, while you know [it is unlawful].}[Quran 2:188]. Moreover, Allaah conditioned consent [between the buyer and seller] in trade for the validity of the transaction. Allaah Says (what means): {…but only [in lawful] business by mutual consent.}[Quran 4:29]. So Allaah clarified many matters which have a relation with economical issues, like conditioning witnesses in sale transactions, recording the debt in writing and the like. For more details, you could refer to the books of Tafseer (interpretation of the Quran) especially those which gave great importance to the verses about the rulings (Islamic Law).

Likewise, the Sunnah of the Prophet is full of rulings related to the economy. It explained in details the forms of Ribaa (usury or interest), the conditions of sale and so forth. 

Allaah Knows best.