According to historical records, Umar b. al-Khattab prided himself on his “improvements” to the teachings of the Qur’an and the Prophet. Although Abu Bakr and Uthman both adjusted religious law for special cases, Umar relied almost entirely on his own opinion and encouraged others to do the same.
When he appointed Shurayh al-Qadi as the religious judge of Madinah, he instructed him, “If you are searching for a verdict, then look in the Book of God. If you do not find one, then look in the tradition of the Prophet. But if you do not find it in the tradition of the Prophet, then make up a verdict yourself.” 
Similarly, he wrote to Abu Musa al-Ashari, “If you do not find an answer in the Book or the tradition, then make an analogy and develop an answer yourself.” For these reasons, al-Tabari says that people preferred not to take their disputes to Umar, because he was known for judging by his personal beliefs, rather than the Islamic criteria.
 For example, Abu Bakr was unwilling to prosecute Khalid b. al-Waleed, who killed Malik b. Nuwayrah, and who on the same night, had committed adultery with the wife of the victim. Abu Bakr said, “He made ijtihad (deducing Muslim law), but of course he made an error,” and left the matter at that.
 Muhammad al-Khudari, Tarikh al-Tashri al-Islami, p.83
 Al-Tabari, 2:617