"Until, when he reached between the two barriers." Qatada said: They are two mountains. "He found beside them a people who could hardly understand a speech." Meaning: the speech of others. It is also recited in another manner: "...who could hardly make their speech understood," meaning: no one could understand their speech.
Surah Al-Kahf (verses 94-98).
﴿حَتَّى إِذَا بَلَغَ بَيْنَ السَّدَّيْنِ﴾ قَالَ قَتَادَةُ: هُمَا جَبَلَانِ ﴿وَجَدَ مِنْ دُونِهِمَا قَوْمًا لَا يَكَادُونَ يفقهُونَ قولا﴾ يَعْنِي: كَلَامَ غَيْرِهِمْ، وَهِيَ تُقْرَأُ عَلَى وَجْهٍ آخَرَ: ﴿لَا يَكَادُونَ يُفْقِهُونَ قَوْلًا﴾ أَيْ: لَا يَفْقَهُ أحد كَلَامهم.
سُورَة الْكَهْف من (آيَة ٩٤ آيَة ٩٨).