Mu'jam Kabir Tabarani 10545 — Heraclius wrote to Mu'awiyah and said

Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrated that Heraclius wrote to Mu'awiyah (may Allah be pleased with him) and said: If any part of prophethood still remains among them, he will certainly tell me about what I am going to ask them. Ibn Abbas (may Allah be pleased with them both) said: So he wrote to Mu'awiyah (may Allah be pleased with him) asking him about the Milky Way and the rainbow, and about the patch of ground on which the sun has fallen for only a single hour. He said: When the letter and the messenger reached Mu'awiyah (may Allah be pleased with him), he said: This is something I never imagined I would be asked about, up to this very day of mine. Who can answer this? It was said: Ibn Abbas. So Mu'awiyah (may Allah be pleased with him) folded up the letter of Heraclius and sent it to Ibn Abbas (may Allah be pleased with them both), who wrote in reply: "The rainbow is a security for the people of the earth against drowning; the Milky Way is the gate of the sky from which it will be split open; and as for the place on which the sun has fallen for only one hour of the day, it is the sea that was parted for the Children of Israel."