How did the science of Fiqh develop?

Muslims used to receive religious rulings directly from the Prophet, peace and blessings be upon him, and the Quran was revealed, giving rulings and clarifying matters. The Prophet, peace and blessings be upon him, approved some Companions for Ijtihad (independent reasoning), and a number of Companions used to issue fatwas during his time. After the death of the Prophet, peace and blessings be upon him, the religion and Fiqh (jurisprudence) continued, and people followed his guidance and the guidance of the Rightly Guided Caliphs. Abu Bakr and Umar, may Allah be pleased with them, used to judge and issue fatwas based on what they found in the Quran and Hadith, or through the Ijtihad of the Companions when a text was unavailable. Then the Companions dispersed into different regions as teachers and mujahideen, and each of them issued fatwas based on what reached them or what their Ijtihad led them to. Among the most famous muftis from the Companions were: Umar, Ali, Ibn Mas'ud, Aisha, Zayd, Ibn Abbas, and Ibn Umar. Then their students, the Tabi'un, graduated from them, followed by the four great Imams: Abu Hanifa, Malik, Al-Shafi'i, and Ahmad ibn Hanbal, whose opinions were recorded and became followed madhhabs (schools of thought). Fiqh has remained rich and comprehensive of all life's issues, and no era is without someone who stands for Allah with proof.