Musnad Ahmad 25:986

Abu Kamil and Hasan ibn Musa narrated to us, they said: Hammad narrated to us, he said: Ammar ibn Abi Ammar informed us. Hasan said: From Ammar. Hammad said: And I think it is from Ibn Abbas—and Hasan did not doubt it—he said: Ibn Abbas said. And Affan narrated to us, Hammad narrated to us, from Ammar ibn Abi Ammar—it is mursal, there is no Ibn Abbas in it—that the Prophet, peace and blessings of Allah be upon him, said to Khadija:—and Affan mentioned the hadith. Abu Kamil and Hasan said in their hadith: That the Prophet, peace and blessings of Allah be upon him, said to Khadija: "I see a light, and I hear a sound, and I fear that there is madness in me." She said: "Allah would not do that to you, O son of Abdullah." Then she went to Waraqah ibn Nawfal and mentioned that to him. He said: "If he is truthful, then this is the Namus (the angel of revelation) like the Namus of Musa. If he is sent while I am alive, I will surely support him, help him, and believe in him."