Surah Al-Kahf — Ayah 97 (18:97)
فَمَا ٱسۡطَٰعُوٓاْ أَن يَظۡهَرُوهُ وَمَا ٱسۡتَطَٰعُواْ لَهُۥ نَقۡبٗا ٩٧
English translation (Saheeh International)
So they [i.e., Gog and Magog] were unable to pass over it, nor were they able [to effect] in it any penetration.
Brief commentary
So Gog and Magog were unable to climb over it due to its height nor were they able to make a hole in it from beneath due to its hardness.