Heard of An Improper Conduct of His Brother
7-10-2018 | IslamWeb
Question:
Recently I got a message from a non-Muslim girl that was in my class last year she told me that she believed that my brother was stalking her and her friends on social media and wanted me to talk to him because she found it very creepy. I told her I wouldn’t do so because I am very shy to talk to my brother about such a matter and also I didn’t believe he would do such a thing. She told me she caught him doing such things in the library. After telling her I don’t want to help her now she also seems to be angry at me. My question is what am I supposed to do? Is it the right thing for me to ask my brother or is it a sin as I’m helping a non Muslim girl? Also I’m worried that my intentions if I ask my brother would be more so to please the girl than for justice, am I also sinful for this? Thank you.
Answer:
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad 
is His slave and Messenger.
There is nothing wrong in merely helping a non-Muslim girl in a permissible matter that she needs help in. Indeed, it is permissible in Islam to be kind to a non-Muslim who is at peace with the Muslims. Allah Says (what means): {Allah does not forbid you from those who do not fight you because of religion and do not expel you from your homes - from being righteous toward them and acting justly toward them. Indeed, Allah loves those who act justly.} [Quran 60:8]
This is in general.
With regard to the incident mentioned in the question, in principle your brother is innocent of what this girl is accusing him of. So, think good of him until the contrary of what you think is proven. Allah Says (what means): {O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin.} [Quran 60:8]
If it is proven that your brother had done what is displeasing to Allah, then it is obligatory to advise him in a good manner. Tameem Ad-Daari 
narrated that the Prophet, sallallaahu ʻalayhi wa sallam, said, “The (essence of) religion is (to offer sincere) advice.” [Muslim]
If your intention in providing advice is sincere to Allah, then there is nothing wrong if the girl is consequently becomes pleased with your advice; this does not contradict sincerity.
Allah knows best.