و من وصية له عليه السلام لعبد الله بن العباس لما بعثه للاحتجاج على الخوارج
لا تخاصمهم بالقرآن فان القرآن حمال ذو وجوه تقول و یقولون و لکن خاصمهم بالسنه فانهم لن یجدوا عنها محیصا
A Letter from Imam Ali (a.s)
[When Imam Ali (a) sent Ibn Abbas for discussions with the Kharijites, he, peace be upon him, gave him the following instructions.]
While arguing, never quote statements from the Holy Qur'an because the passages of this Book require very careful consideration as they could be paraphrased in various ways and their meanings could be construed differently. Thus, you will adhere to your explanation and they will stick to their elucidation. Therefore, argue with them in the light of the traditions of the Holy Prophet (s) and then they will find no way to misrepresent truth.