1 Haraam looking. Allaah has commanded both believing men and believing women to lower their gaze. He says (interpretation of the meaning):
Tell the believing men to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts). That is purer for them. Verily, Allaah is All‑Aware of what they do.
31. And tell the believing women to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts) and not to show off their adornment except only that which is apparent
[al-Noor 24:30-31]
In Saheeh Muslim (2159) it is narrated that Jareer ibn Abd-Allaah (may Allaah have mercy on him) said: I asked the Messenger of Allaah (peace and blessings of Allaah be upon him) about an accidental glance and he ordered me to avert my gaze.
2 It may result in haraam touching., which includes shaking hands. The Prophet (peace and blessings of Allaah be upon him) said: If one of you were to be stabbed in the head with an iron needle, that would be better for him than his touching a woman who is not permissible for him. Narrated by al-Tabaraani from Maqil ibn Yasaar; classed as saheeh by al-Albaani in Saheeh al-Jaami no. 5045.
3 Mixing may lead to a man being alone with a non-mahram woman, which is haraam because the Prophet (peace and blessings of Allaah be upon him) said: No man is alone with a woman but the third one present is the shaytaan. Narated by al-Tirmidhi (2165); classed as saheeh by al-Albaani in Saheeh al-Tirmidhi.
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