Answer: Yes, it is necessary (wajib) to cover one’s minimum nakedness (between the navel and knee for both men and women), even when alone. The exception is when there is a need, such as taking a shower, relieving oneself, or changing one’s clothes. Even in such situations, it is recommended to minimize the exposure.
Furthermore, although it is permissible for spouses to look at any part of their partner’s body, it is disliked that they become completely naked during cohabitation. They should cover themselves with a sheet or covering.
قَالَ: قُلْتُ: يَا رَسُولَ اللهِ عَوْرَاتُنَا مَا نَأْتِي مِنْهَا وَمَا نَذَرُ؟ قَالَ: احْفَظْ عَوْرَتَكَ إِلاَّ مِنْ زَوْجَتِكَ أَوْ مَا مَلَكَتْ يَمِينُكَ، فَقَالَ: الرَّجُلُ يَكُونُ مَعَ الرَّجُلِ؟ قَالَ: إِنْ اسْتَطَعْتَ أَنْ لاَ يَرَاهَا أَحَدٌ فَافْعَلْ، قُلْتُ: وَالرَّجُلُ يَكُونُ خَالِيًا، قَالَ: فَاللَّهُ أَحَقُّ أَنْ يُسْتَحْيَا مِنْهُ (ترمذي)
Narrated Bahz bin Hakim: “My father narrated to me from my grandfather, who said: ‘I said: “O Messenger of Allah! Regarding our ‘Awrah, what of it must we cover, and what of it may we leave?” He said: “Protect your ‘Awrah except from your wife or what your right hand possesses.”‘ He said: “What about a man with another man?” He said: “If you are able to not let anyone see it, then do so.” I said: “What about a man when he is alone?” He said: “Allah is most deserving of being shy from Him.” [ Tirmidhi]
وسيذكر شروط الستر والساتر ( قوله ووجوبه عام) اي في الصلاة وخارجها ( قوله ولو في الخلوة ) اي اذا كان خارج الصلاة يجب الستر بحضرة الناس اجماعاً وفي الخلوة على الصحيح – رد المحتار ج٣ ص ٢٥٠
And Almighty Allah Knows Best