Hadith: The Prophet (may Allah’s peace and blessings be upon him) mentioned something and said: "That will be at the time when knowledge disappears

عَنْ زِيَادِ بْنِ لَبِيدٍ رضي الله عنه قَالَ:
ذَكَرَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ شَيْئًا، فَقَالَ: «ذَاكَ عِنْدَ أَوَانِ ذَهَابِ الْعِلْمِ» قُلْتُ: يَا رَسُولَ اللَّهِ، وَكَيْفَ يَذْهَبُ الْعِلْمُ، وَنَحْنُ نَقْرَأُ الْقُرْآنَ وَنُقْرِئُهُ أَبْنَاءَنَا وَيُقْرِئُهُ أَبْنَاؤُنَا أَبْنَاءَهُمْ إِلَى يَوْمِ الْقِيَامَةِ؟ قَالَ: «ثَكِلَتْكَ أُمُّكَ زِيَادُ، إِنْ كُنْتُ لَأُرَاكَ مِنْ أَفْقَهِ رَجُلٍ بِالْمَدِينَةِ، أَوَلَيْسَ هَذِهِ الْيَهُودُ وَالنَّصَارَى يَقْرَؤونَ التَّوْرَاةَ وَالْإِنْجِيلَ، لَا يَعْمَلُونَ بِشَيْءٍ مِمَّا فِيهِمَا؟!».
[صحيح لغيره] - [رواه ابن ماجه] - [سنن ابن ماجه: 4048]

Ziyād ibn Labīd (may Allah be pleased with him) reported:
The Prophet (may Allah’s peace and blessings be upon him) mentioned something and said: "That will be at the time when knowledge disappears." I said: "O Messenger of Allah, how will knowledge disappear when we recite the Qur’an and teach it to our children, and they teach it to their children (and so on) until the Day of Judgment?" He said: "May your mother be bereaved of you, O Ziyād! I thought you were the most knowledgeable man in Madīnah. Is it not the case with these Jews and Christians who read the Torah and the Gospel, yet they do not act upon anything therein?!"
[Authentic by Another chain of narrators] - [Narrated by Ibn Majah] - [Sunan Ibn Majah - 4048]

Explanation

As the Prophet (may Allah's peace and blessings be upon him) was sitting among his Companions, he said: This is the time at which knowledge will disappear and be taken away from people. Thereupon, Ziyād ibn Labīd al-Ansāri (may Allah be pleased with him) wondered and asked the Prophet (may Allah's peace and blessings be upon him): How will knowledge be taken away from us and we lose it, whereas we recite and memorize the Qur’an?! By Allah, we will recite it and make our women and children and our children's children recite it. In response, the Prophet (may Allah's peace and blessings be upon him) said in wonder: May your mother be bereaved of you, O Ziyād! I considered you to be among the knowledgeable people of Madīnah. Then, the Prophet (may Allah's peace and blessings be upon him) pointed out that knowledge will not be lost by the loss of the Qur’an, but knowledge will be lost by the loss of acting upon it. A case in point is the Jews and the Christians, who have the Torah and the Gospel, yet they did not derive benefit from them or their objective, namely acting upon what they have learned.