Quran 7:134 — The Purgatory (Al-A'araf)

وَلَمّا وَقَعَ عَلَيهِمُ الرِّجزُ قالوا يٰموسَى ادعُ لَنا رَبَّكَ بِما عَهِدَ عِندَكَ ۖ لَـِٔن كَشَفتَ عَنَّا الرِّجزَ لَنُؤمِنَنَّ لَكَ وَلَنُرسِلَنَّ مَعَكَ بَنى إِسرٰءيلَ

Whenever a plague afflicted them, they said, "O Moses, implore your Lord—you are close to Him. If you relieve this plague, we will believe with you, and will send the Children of Israel with you."

[7:133] Consequently, we sent upon them the flood, the locusts, the lice, the frogs, and the blood—profound signs. But they maintained their arrogance. They were evil people.

[7:135] Yet, when we relieved the plague for any length of time, they violated their pledge.