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What does Islam say about being friends with the opposite sex?

What does Islam say about being friends with the opposite sex? Please, could you include references as well, and if it is not correct then what should one do about the people they are already friends with?

Answer

Given the Islamic guidance on man-woman relationship, I am of the view that a woman can’t make a non-mahram man her friend. She can benefit from his talents (and vice versa) within the limits imposed by Islamic teachings. To be a friend calls upon the two individuals to be close to each other, both emotionally and, on most occasions, physically. That kind of intimacy is something not possible to have with a member of opposite gender if you are genuinely following the teachings of Islam.
The following are only a few of the many Quranic verses and ahadith on the subject that have helped me in coming to the above-mentioned conclusion.
“And come not near unto adultery. Lo! it is an abomination and an evil way.” (17:32)
“Enjoin the believing men to lower their gaze and guard their modesty; that is chaster for them. Surely Allah is well aware of their actions. Likewise enjoin the believing women to lower their gaze and guard their modesty; not to display their beauty and ornaments except what normally appears thereof; let them draw their veils over their bosoms and not display their charms except to their husbands, their fathers, their fathers-in-law, their own sons, their stepsons, their own brothers, their nephews on either brothers’ or sisters’ sides, their own womenfolk, their own slaves, male attendants who lack sexual desires or small children who have no carnal knowledge of women. Also enjoin them not to strike their feet in order to draw attention to their hidden trinkets. And O believers! Turn to Allah in repentance, all of you, about your past mistakes, so that you may attain salvation.” (24:30-31)
Narrated Abdullah bin Abbas: “Al-Fadl (his brother) was riding behind Allah’s Apostle and a woman from the tribe of Khath’am came and Al-Fadl started looking at her and she started looking at him. The Prophet turned Al-Fadl’s face to the other side.” (Bukhari)
Narrated Ibn Abbas: “That he heard the Prophet saying, ‘ It is not permissible for a man to be alone with a woman, and no lady should travel except with a Muhram (i.e. her husband or a person whom she cannot marry in any case for ever; e.g. her father, brother, etc.).’ Then a man got up and said, “O Allah’s Apostle! I have enlisted in the army for such-and-such ghazwa and my wife is proceeding for Hajj.’ Allah’s Apostle said, ‘ Go, and perform the Hajj with your wife.'”
If you have a friend / friends from the opposite sex, try to reduce the frequency of interaction with him / them. Avoid being in their company alone with immediate effect. You can tell them plainly that such a possibility is out of question. Mention that you have come to this decision through your religious understanding. Mention everything politely but clearly. Pray to the Almighty to help you out in your efforts. You will see that the more you are moving towards the Almighty’s way, the more you are getting stronger from inside. May the Almighty help you in your firm resolve.