Quran 7:106 — The Purgatory (Al-A'araf)

He said, "If you have a sign, then produce it, if you are truthful."

[7:105] "It is incumbent upon me that I do not say about GOD except the truth. I come to you with a sign from your Lord; let the Children of Israel go."

[7:107] He threw down his staff, and it turned into a tremendous serpent.