The Prophet (peace and blessings of Allah be upon him) realized the law of change in life, so he encouraged his companions to exercise ijtihad, so that they would know the ruling on new events that were renewed with life. The companions followed the approach that the Messenger of Allah (peace and blessings of Allah be upon him) drew for them, and they were the first people to follow his approach and imitate his conduct. They had many ijtihads in various aspects of life, and their approach was to interact with issues that needed a ruling, whether these issues were in politics, the judiciary, worship, transactions, or personal status. They thus opened the door of ijtihad for the scholars who came after them, and the scholars remained on this path until eras ended and their opinions were recorded and they became widely used. Then some scholars saw that these schools of thought were sufficient, and that the Muslim must adhere to one of them, and that there is no mujtahid after the imams of the schools of thought.