The ruling on a male student greeting his female classmates in the college

Question:
I am a university student, and sometimes I greet the girls. Is it lawful or forbidden for a male student to greet his female classmate in the college?

Answer:
First, it is not permissible to study with girls in the same place or the same school; rather, this is one of the greatest causes of fitnah (trial, discord or temptation). Therefore, this joint attendance is not permissible for the male student or the female student because of the fitnah involved.
As for the greeting, there is nothing wrong with his greeting her with a Shari'ah-compliant greeting that does not expose her to causes of fitnah. There is no blame on her for greeting him as well, provided there is no handshaking, because handshaking is not permissible for a non-mahram (a relative one may not marry). Rather, the greeting should be from a distance, with hijab (the covering prescribed for women), away from causes of fitnah, and without seclusion. A Shari'ah-compliant greeting that does not involve fitnah is permissible.
However, if the greeting to her causes fitnah, or if her greeting to him does so—meaning it is driven by desire or longing for what Allah has forbidden—then this is prohibited by the Shari'ah. And success is from Allah.