(Addariyath) 51 : 37
وَتَرَكْنَا فِيهَا آيَةً لِلَّذِينَ يَخَافُونَ الْعَذَابَ الْأَلِيمَ
And We left therein a sign for those who are fearing painful punishment.
The Dead sea is the sign left behind being a sign for the coming generations. See explanation 7: 84; 15: 75; 53: and 53-54.