Is there sin upon a university student if his gaze unintentionally falls upon girls at the university, and he then lowers his gaze?

As for studying in mixed universities and schools, the default ruling is that it is strictly forbidden due to the great temptations and grave corruptions it entails. Therefore, it is obligatory for Muslim men and women to avoid them and seek education free from mixing. However, if there is no other way for a Muslim to complete their education or obtain a degree necessary for their religious or worldly life except through these universities and schools, and they are truly compelled to do so, such that they would most likely face severe hardship and difficulty if they do not study, then it is permissible for them to study there, provided they fully adhere to Islamic regulations. The most important of these are:

1. That the motive for studying is to obtain a degree and beneficial knowledge, not merely to pass time, for amusement, or entertainment. 2. That the student is strong in their faith and confident in themselves, such that they are safe from falling into temptation; otherwise, studying is not permissible for them. 3. To commit to lowering the gaze from everything that Allah Almighty has forbidden. 4. To commit to wearing lawful clothing. If it is a woman, she must adhere to the lawful hijab that covers the entire body, is not transparent or tight, and does not reveal the body's attractions. Wearing the niqab (face veil) is not a condition unless she fears temptation. 5. Not to mix with non-mahrams (unmarriageable kin), to keep away from them as much as possible, and not to engage in any conversation with them except out of extreme necessity and within the bounds of proper conduct. 6. Not to be in seclusion with any non-mahram man, and to stay away from places of seclusion. 7. That this study does not lead to engaging in anything forbidden, such as learning music, sculpture, or other forbidden matters. 8. If it is a woman, she must be accompanied by a mahram if the distance she travels for study is a travel distance (qasr), which is approximately 83 kilometers or more. If it is less than that, she is not required to have a mahram, but it is not permissible for her to travel without a mahram except in cases of urgent necessity that cannot be avoided. 9. To be safe from falling into immoralities, vices, or being impressed by anything forbidden. 10. To be capable of adhering to Islamic commands and avoiding prohibitions, and not to fall into forbidden acts. 11. To be able to reconcile their studies with their future work. 12. To be able to reconcile their studies with matters of their religion, such as prayer, fasting, zakat, and Hajj. 13. To be able to reconcile their studies with caring for their family and household. 14. To be able to reconcile their studies with serving their community and nation. 15. To be able to reconcile their studies with calling to Allah Almighty. 16. To be able to reconcile their studies with enjoining good and forbidding evil. 17. To be able to reconcile their studies with striving in the way of Allah Almighty. 18. To be able to reconcile their studies with working to support Islam and Muslims. 19. To be able to reconcile their studies with working to spread goodness and virtue. 20. To be able to reconcile their studies with working to combat evil and vice. 21. To be able to reconcile their studies with working to uphold the word of Allah Almighty. 22. To be able to reconcile their studies with working to elevate the status of Muslims. 23. To be able to reconcile their studies with working to achieve justice and fairness. 24. To be able to reconcile their studies with working to establish security and stability. 25. To be able to reconcile their studies with working to spread knowledge and learning. 26. To be able to reconcile their studies with working for the progress and prosperity of society. 27. To be able to reconcile their studies with working to build civilization and advancement. 28. To be able to reconcile their studies with working to spread peace and harmony. 29. To be able to reconcile their studies with working to achieve happiness and contentment. 30. To be able to reconcile their studies with working to win Paradise and be saved from Hellfire. 31. To be able to reconcile their studies with working to gain the pleasure of Allah Almighty. 32. To be able to reconcile their studies with working to achieve the ultimate goal, which is the worship of Allah Almighty. 33. To be able to reconcile their studies with working to uphold the word of Tawhid (monotheism) and spread the Sunnah. 34. To be able to reconcile their studies with working to combat polytheism and innovations. 35. To be able to reconcile their studies with working to spread virtue and good morals. 36. To be able to reconcile their studies with working to combat vice and reprehensible morals. 37. To be able to reconcile their studies with working to establish religion and defend it. 38. To be able to reconcile their studies with working to support the oppressed and aid the distressed. 39. To be able to reconcile their studies with working to help the needy and assist the weak. 40. To be able to reconcile their studies with working to spread justice and equality. 41. To be able to reconcile their studies with working to combat oppression and tyranny. 42. To be able to reconcile their studies with working to establish the foundations of security and stability. 43. To be able to reconcile their studies with working to build and develop society. 44. To be able to reconcile their studies with working to spread beneficial knowledge and useful information. 45. To be able to reconcile their studies with working to educate generations and prepare them for the future. 46. To be able to reconcile their studies with working to build the nation and unite its ranks. 47. To be able to reconcile their studies with working to achieve unity and solidarity among Muslims. 48. To be able to reconcile their studies with working to spread a culture of tolerance and coexistence. 49. To be able to reconcile their studies with working to combat fanaticism and extremism. 50. To be able to reconcile their studies with working to spread the values of peace and love. 51. To be able to reconcile their studies with working to achieve happiness in this world and the Hereafter. 52. To be able to reconcile their studies with working to gain the pleasure of Allah Almighty and win Paradise.