Hadith: There is no god but Allah. Woe to the Arabs from an impending evil. Today, an opening has been made in the wall of Gog and Magog, like this,

عَنْ زَيْنَبَ بِنْتِ جَحْشٍ رَضِيَ اللَّهُ عَنْها أَنَّ النَّبِيَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ دَخَلَ عَلَيْهَا فَزِعًا يَقُولُ:
«لاَ إِلَهَ إِلَّا اللَّهُ، وَيْلٌ لِلْعَرَبِ مِنْ شَرٍّ قَدِ اقْتَرَبَ، فُتِحَ اليَوْمَ مِنْ رَدْمِ يَأْجُوجَ وَمَأْجُوجَ مِثْلُ هَذِهِ» وَحَلَّقَ بِإِصْبَعِهِ الإِبْهَامِ وَالَّتِي تَلِيهَا، قَالَتْ زَيْنَبُ بِنْتُ جَحْشٍ فَقُلْتُ يَا رَسُولَ اللَّهِ: أَنَهْلِكُ وَفِينَا الصَّالِحُونَ؟ قَالَ: «نَعَمْ إِذَا كَثُرَ الخَبَثُ».
[صحيح] - [متفق عليه] - [صحيح البخاري: 3346]

Zaynab bint Jahsh (may Allah be pleased with her) reported: The Prophet (may Allah's peace and blessings be upon him) came to her in an alarmed state, saying:
"There is no god but Allah. Woe to the Arabs from an impending evil. Today, an opening has been made in the wall of Gog and Magog, like this," making a circle with his thumb and index fingers. Zaynab bint Jahsh said: So, I said: "O Messenger of Allah, shall we perish while there are pious people among us?" He said: "Yes, when wickedness becomes rampant."
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Bukhari - 3346]

Explanation

The Prophet (may Allah's peace and blessings be upon him) entered the place of Zaynab bint Jahsh (may Allah be pleased with her) terrified and afraid, while he was saying: There is no god but Allah, indicating the expectation of something unpleasant happening, and that there is no escape from it except by seeking refuge in Allah Almighty. Then, he (may Allah's peace and blessings be upon him) said: Woe to the Arabs from an evil that is about to happen. Today, a hole has been opened in the dam of Gog and Magog, which was built by Dhu al-Qarnayn, like this, as he made a circle with his thumb and the one next to it. Zaynab (may Allah be pleased with her) said: How can Allah send destruction upon us when there are righteous believers among us? The Prophet (may Allah's peace and blessings be upon him) responded to her, saying: If evil, such as immorality, debauchery, sins, adultery, alcohol, and other things, becomes widespread, destruction will befall everyone.