Surat Al-Kahf (The Cave) - الكهف

ءَاتُونِى زُبَرَ ٱلْحَدِيدِ حَتَّىٰٓ إِذَا سَاوَىٰ بَيْنَ ٱلصَّدَفَيْنِ قَالَ ٱنفُخُوا۟ حَتَّىٰٓ إِذَا جَعَلَهُۥ نَارًا قَالَ ءَاتُونِىٓ أُفْرِغْ عَلَيْهِ قِطْرًا ﴿٩٦﴾ فَمَا ٱسْطَٰعُوٓا۟ أَن يَظْهَرُوهُ وَمَا ٱسْتَطَٰعُوا۟ لَهُۥ نَقْبًا﴿٩٧﴾

Bring me blocks of iron; until when he had filled up the space between the two mountain sides, he said: Blow, until when he had made it (as) fire, he said: Bring me molten brass which I may pour over it. So they were not able to scale it nor could they make a hole in it.