An Example of a Valid Ijtihad vs. An Invalid Ijtihad
“And ‘Ammar (bin Yasir) was killed by Abu al-Ghadiyah Yasar bin Sab’ as-Sulami. Abu al-Ghadiyah attended Bay’at ar-Ridwan, so, Allah witnessed what was in his heart, descended tranquility upon him, and was Pleased with him. So, Abu al-Ghadiyah made a false interpretation (ta’wil), and made a mistaken and incorrect ijtihad, for which he will get one reward.
This is not the case with the killers of ‘Uthman, as there was no room for ijtihad in killing him, as he had not killed anyone, nor made war or fought against anyone, nor even defended himself against anyone, nor committed adultery, nor apostated. So, those who fought him had no rational interpretation whatsoever that they could use to justify their actions. Rather, they are rebellious, sinning warmongers who intentionally spilt sacred blood – without any valid justification – simply out of oppression and enmity. So, they are accursed sinners.”
[‘al-Fisal fil-Milal wan-Nihal’; 4/161]