Surah An-Naml 27:44

قِيلَ لَهَا ٱدْخُلِى ٱلصَّرْحَ ۖ فَلَمَّا رَأَتْهُ حَسِبَتْهُ لُجَّةً وَكَشَفَتْ عَن سَاقَيْهَا ۚ قَالَ إِنَّهُۥ صَرْحٌ مُّمَرَّدٌ مِّن قَوَارِيرَ ۗ قَالَتْ رَبِّ إِنِّى ظَلَمْتُ نَفْسِى وَأَسْلَمْتُ مَعَ سُلَيْمَـٰنَ لِلَّهِ رَبِّ ٱلْعَـٰلَمِينَ

She was told, "Enter the palace." But when she saw it, she thought it was a body of water and uncovered her shins [to wade through]. He said, "Indeed, it is a palace [whose floor is] made smooth with glass." She said, "My Lord, indeed I have wronged myself, and I submit with Solomon to Allāh, Lord of the worlds."

Translation: Saheeh International

Tafsir

It was also said to her ‘Enter the palace hallway’ — this was a transparent white glass floor underneath which flowed sweet water that contained fish. Solomon had it made when he was told that her legs and feet resembled the shanks of a mule. …

Excerpt from Tafsir al-Jalalayn, commentary on 27:44, via Quran.com. The reader has the full commentary and 9 more tafsirs.