Musannaf Ibn Abi Shayba 36:20

Ali ibn Mushir narrated to us, from Abu Ishaq al-Shaybani, from Abdullah ibn Shaddad ibn al-Had, who said: Gabriel descended upon the Messenger of Allah, may Allah bless him and grant him peace, and then said: "Read." He said: "What shall I read?" He said: Then he embraced him, then said to him: "Read." He said: "What shall I read?" He said: "Read in the name of your Lord who created." So he came to Khadijah and informed her of what he had seen. She went to Waraqah ibn Nawfal and mentioned that to him. He said to her: "Has your husband seen his companion while awake?" She said: "Yes." He said: "Then your husband is a prophet; he will be afflicted by a trial from his nation."