It is obligatory to wear clothes while offering As-Salat (the prayers)

وَقَوْلِ اللَّهِ تَعَالَى: {خُذُوا زِينَتَكُمْ عِنْدَ كُلِّ مَسْجِدٍ}. وَمَنْ صَلَّى مُلْتَحِفًا فِي ثَوْبٍ وَاحِدٍ، وَيُذْكَرُ عَنْ سَلَمَةَ بْنِ الأَكْوَعِ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «يَزُرُّهُ وَلَوْ بِشَوْكَةٍ». فِي إِسْنَادِهِ نَظَرٌ، وَمَنْ صَلَّى فِي الثَّوْبِ الَّذِي يُجَامِعُ فِيهِ مَا لَمْ يَرَ أَذًى، وَأَمَرَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَنْ لاَ يَطُوفَ بِالْبَيْتِ عُرْيَانٌ.And the Statement of Allah تعالى: “Take your adornment (by wearing your clean clothes covering completely the Aurah): [It means, while offering Salat (prayer), a male must cover himself with clothes from the umbilicus of his abdomen up to his knees, and it is better that both his shoulders should be covered. A female must cover all her body and feet, except the face, and it is better that both her hands are also covered.] While praying and going around (the Tawaf of) the Ka‘bah (V.7:31). And offering Salat while wearing a single garment wrapped around the body, Salma bin Al-Akwa‘ narrated: The Prophet ﷺ said, “He should pin it, even if with a thorn.” Offering Salat with the same garment in which one has had sexual intercourse is permissible if one does not see anything dirty on it. The Prophet ﷺ ordered that no one should go around the Ka‘bah (perform Tawaf) in a naked state.