Is arguing online a sin in Islam?
You would never say it to his face. You said it anyway.

It is half past midnight. Somebody has posted something you think is stupid, and you are lying in the dark writing a reply.
You would never walk up to that man in a shop and say it to his face. But it takes four seconds here and you feel nothing while you do it.
Does what I type count the same as what I say?
Yes. Nabi ﷺ said whoever believes in Allah and the Last Day should say something good, or stay quiet.
It does not stop applying because you typed it instead of saying it. He still reads it. He still feels it. The distance only took away the part of you that would have stopped.
Nabi ﷺ also said a person can say one word without thinking whether it is right or wrong, and it drags him down into the Fire further than the distance between east and west.
One word, said without thinking. That is most of what gets posted at midnight.
The screen did not change the ruling. It just took away the awkwardness that used to keep you polite.
What does the Quran say about how we talk to each other?
One short chapter covers almost all of it.
Do not mock other people. They may be better than you. Do not insult each other or call each other names.
Do not spy on each other or talk about each other behind their backs. Allah asks if any of you would like to eat the flesh of his dead brother. You would hate it.
And when someone brings you news, check it before you act on it, or you may hurt people without knowing and regret it. That includes pressing share.
Is it backbiting if it is true?
Yes. Nabi ﷺ said backbiting is saying something about your brother that he would not like. He was asked: what if it is true? He said: if it is true, that is backbiting. If it is not true, that is worse. You have lied about him.
So the thread about what someone said, or the screenshot of their mistake, does not become fine because it really happened.
What if I am arguing for the deen?
Some of the ugliest talk online is between Muslims, about religion, in public. People who would never insult someone inside a masjid do it freely under a post and call it defending the truth.
You can be completely right and still answer for how you said it.
Nabi ﷺ promised a house on the edge of Paradise for the person who leaves an argument, even when he is right.
Even when he is right. Walking away from a winning argument is something he promised a reward for.
What to do
- Read it back and imagine saying it to his face in a room with other people listening. If you would not, do not post it.
- Wait until the morning before replying to anything that made your chest tight.
- Check a story before you share it. If you cannot check it, do not pass it on.
- Correct people privately where you can. Correcting somebody in public is mostly for the audience.
What not to do
- Do not join a pile-on. Everyone in it thinks they only added one comment.
- Do not screenshot somebody's private message to make a point. They trusted you with it.
- Do not use religion as cover for insulting people. Everybody can tell, including you.
One last thing
The hadith gives two options. Say something good, or say nothing. Saying nothing is a complete answer, and it is still there at midnight.
The next time you catch yourself typing a reply in the dark, put the phone face down and go to sleep. Read it again in the morning.
Source: Sahih al-Bukhari 6018; Sahih al-Bukhari 6477; Quran 49:11; Quran 49:12; Quran 49:6; Sahih Muslim 2589; Sunan Abi Dawud 4800 (hasan per al-Albani)
SM
The teaching in this post comes from the Quran and the hadith listed above. I only put it in plain words. The tips on what to do and what not to do are my own advice. If you want to talk about anything in this post, write to me at salam@sunnahdaily.com.
For a ruling on your own situation, please speak to a qualified local scholar. You are welcome to email me about it as well, and I will help if I can, or point you to someone who can.