A narration from the Messenger of Allah is as follows:
Messenger of Allah said: “I forbid you to be alone with women.”
A man asked: “What about the relatives of her husband?”
Messenger of Allah: “Being alone with them is death!” (Bukhari, Nikah/Marriage, 112)
Allah the Almighty commands about women:
“Tell the believing women to reduce some of their looks, and cover their private parts. Tell them not to uncover their beautiful parts except what is naturally seen. Tell them to put their headscarves onto their chests and not expose their beautiful parts except to their husbands, their fathers, their husbands’ fathers, their sons, their husbands’ sons, their brothers, their brothers’ sons, their sisters’ sons, their women, those in their possession, those male attendants that have no sexual desire to women, or children who are not yet aware of the private aspects of women. And tell them not to stamp their feet on the ground for their beautiful parts to be noticed. Believers! Return all together towards Allah, so that you may attain what you hope for.” (An-Nur/ The Light 24:31)
According to these information, a woman can only be alone and uncovered with these men which are mentioned above. Apart from this, all men are considered strangers for a Muslim woman even though they are relatives. She is allowed to be and talk with them in public areas and she should be covered whenever in sight of them.
Muslims should avoid things that pave the way for what is unlawful. Allah uses phrases like “do not approach” or “stay away from” while speaking about certain big sins.
He says about adultery:
“Do not approach unlawful sexual intercourse. Indeed, it is an outrageous act and an evil way.” (Al-Isra/ The Night Journey 17:32)
“Not approaching” can only be accomplished by putting a distance between us and the mentioned act. The foregoing 31st verse of chapter Nur clearly describes the measures for this distance.
Someone that leaves his/her house to an unmarried couple, surely provides an environment for a sin to occur. Allah the Almighty says:
“Who intercedes in a good cause shall have a share from it; and who intercedes in an evil cause shall have a burden from it. Allah is always the watcher of everything.” (An-Nisa/ The Women 4:85)
“(…) Help one another in righteousness and in avoiding unlawful things. Do not help one another in sin and transgression. Fear Allah! Surely Allah is severe in retribution.” (Al-Maida/ The Feast 5:2)