Why is it impermissible for a man to enter the house of a woman who is not his wife, sister, daughter, or mother? What is the ruling on a father visiting his adult daughter (16 years old) who lives with his ex-wife, a foreign woman who is still single, especially given the mother's refusal of such a visit?

Islam has forbidden a man from entering upon a non-mahram woman who is neither his wife nor one of his unmarriageable kin, due to the corrupting influences inherent therein. Thus, the prohibition of khalwah (private seclusion) with a non-mahram woman came, because Satan is the third party between them. An exception to this is when khalwah occurs with assurance of safety from fitna (temptation). The Holy Quran has clarified the seriousness of khalwah through the story of Prophet Yusuf (peace be upon him) with the wife of Al-Aziz, and how Yusuf (peace be upon him) protected himself with a clear proof from his Lord. This demonstrates the importance of avoiding khalwah even if the person is among the pious, because it opens a door for Satan. Therefore, a man’s abstention from visiting the woman and her daughter, especially given a previous illicit relationship between him and this woman, is precisely the correct and pious course of action. Even the presence of the daughter does not prevent temptation, as Satan may strive to lead them back to sin.