At universities

Answer – and Allah is the One who grants success: The mixing of the sexes is an evil, and in it there is corruption for both sexes, especially with prolonged sitting together, continued conversation, and friendly socializing. In the hadith narrated from the Prophet Muhammad (May Allah bless him and his family and grant them peace): “I have not left after me any trial more harmful to men than women,” or as he said. And it is narrated from him (May Allah bless him and his family and grant them peace): “Women are [weak in] reason and [are] private parts, so conceal their weakness with silence and their private parts with staying in the houses,” or as he said.
And Allah, Exalted is He, commanded the wives of the Prophet (May Allah bless him and his family and grant them peace) to remain settled in the depths of their homes, so He said: "And abide in your homes and do not display yourselves as [was] the display of the former times of ignorance." [al-Ahzab:33] And He, Exalted is He, said: "And when you ask them for any goods, ask them from behind a partition. That is purer for your hearts and their hearts." [al-Ahzab:53] And He commanded the men to lower their gazes, so He said: "Tell the believing men to lower their gaze and guard their private parts. That is purer for them." [an-Nur:30] And He commanded the women just as He commanded the men, so He said: "And tell the believing women to lower their gaze and guard their private parts" [an-Nur:31], and He commanded them to conceal their adornment, so He said: "and not expose their adornment except that which [necessarily] appears thereof … and not expose their adornment except to their husbands, their fathers, their husbands’ fathers, their sons, their husbands’ sons, their brothers …" until His saying, Exalted is He: "And let them not stamp their feet to make known what they conceal of their adornment. And turn to Allah in repentance, all of you, O believers, that you might succeed." [an-Nur:31]
Thus Allah, Exalted is He, directed the believing men and believing women, and expounded the verses for them in this regard, in order to block the avenues of temptation through which Satan may find an entry. For you see in the first verse that Allah, Exalted is He – and He is the All-Knowing, All-Wise – has forbidden believing women from exposing their adornment to immoral and suspicious women, and did not grant them concession to expose their adornment except to “their women”, and they are the believing women.
Therefore we say: What occurs in the university of mixing between the sexes, and what follows it of conversations and socializing, is a great evil, disobedience to Allah, Exalted is He, and opposition to His commands and teachings. It is not lawful for anyone who believes in Allah and the Last Day to attend such gatherings, except in the case that he is denouncing it or changing it.
And for the likes of this Allah cursed the Children of Israel, so He, Sublime is He, said: "Cursed were those who disbelieved among the Children of Israel by the tongue of David and of Jesus, the son of Mary. That was because they disobeyed and [habitually] transgressed. They used not to prevent one another from wrongdoing that they did. How wretched was that which they were doing." [al-Ma’idah:78–79]

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2