Tafsir of Ad-Dhariyat 51:37

"And We left therein" — that is, in the towns — "a sign," meaning a mark indicating what befell them of punishment. Ibn Jurayj said: It is a collection of stacked stones. It was also said: It refers to the very stones with which they were destroyed. Others said: It is a foul-smelling body of water; Al-Shihab remarked that it is as if this refers to the Sea of Galilee. Abu Hayyan permitted the possibility that the pronoun "therein" refers to the act of destruction itself, as it is among the wonders of annihilation—namely, by making the tops of the towns their bottoms and raining down stones upon them. However, the first interpretation is the most apparent.

"For those who fear the painful punishment," meaning those whose nature it is to fear it due to the soundness of their inherent disposition (fitra) and the tenderness of their hearts, unlike others who possess hardened hearts, for they do not pay heed to it, nor do they consider it a sign.