This letter is from Imam Ali (a.s.) to Abdullah Ibn Abbas, whom he sent to debate with the Khawarij. This letter was written during a time when the Khawarij had revolted against Imam Ali (a.s.) and raised objections to his decisions. The Khawarij were a group that became extremist in their pursuit of simplicity in religion and the truth, which posed a challenge to Imam Ali (a.s.).

Imam Ali (a.s.) instructed Ibn Abbas not to argue with the Khawarij based on the Qur'an. The reason for this is that the Qur'an contains multiple meanings and interpretations, and each side could present its own understanding. This would lead to a fruitless debate, with both parties merely repeating their own viewpoints.

Instead, Imam Ali (a.s.) advised Ibn Abbas to argue based on Hadith. The rationale behind this is that the Khawarij had a limited understanding of the significance of Hadith and would not have solid counterarguments to it. This instruction reflects Imam Ali's (a.s.) wisdom and insight into how to engage with different schools of thought.

From this letter, we learn the importance of approaching discussions with wisdom and insight, especially when dealing with differing beliefs and opinions. It emphasizes the need to find common ground and effective methods of communication that can lead to productive dialogue rather than endless disputes.