Al-Kahf 18:97

Fama istaAAoo an yathharoohuwama istataAAoo lahu naqba

So they [i.e., Gog and Magog] were unable to pass over it, nor were they able [to effect] in it any penetration.

So they (Ya’jūj and Ma’jūj) were not able to climb it, nor were they able to make a hole in it.