(Devarim 13:3) "And there shall materialize the sign and the wonder of which he spoke to you, etc.": R. Yossi Haglili said: See how far Scripture penetrated to the ends of the psyche of the idolators and gave them dominion — Even if they cause sun and moon, stars and constellation, to stand still, pay them no heed. Why? (Ibid. 4) "For the L-rd your G-d is trying you to know whether you love the L-rd your G-d, etc."
R. Akiva said: G-d forbid that He should cause them to stand still for the idolators. The verse speaks only of one who was a true prophet in the beginning, (at which time he caused them to stand still, and then became a false prophet, like Chananiah ben Azur (viz. Jeremiah 28).
"Do not pay heed to the words of that prophet": and not (i.e., you may pay heed to the words of) one (such as he) who retracts (his false prophecy).
"or that dreamer of dreams": and he is not suspected retroactively.
For the LORD your God is testing you to see whether you really love etc.