Ibn Ishāq said: Ismāʿīl ibn Abī Ḥakīm told me that it had reached him from Khadījah that she said, “O cousin, can you let me know when your Companion comes to you?”
When the Companion came, he ﷺ said, “O Khadījah, this is Jibrīl.”
She replied, “Sit on my right thigh.”
He did so. She asked, “Do you see him?”
He said, “Yes.”
She said, “Now move over to my left thigh.”
He moved, and she asked again, “Do you see him?”
He said, “Yes.”
Then she removed her head-scarf and uncovered her chest and said, “Do you see him now?”
He answered, “No.”
She said, “Rejoice, for by Allah, he is an angel and not a devil.” (1)

Ibn ʿAbd al-Barr said: It has been narrated through several chains that the Prophet ﷺ said, “O Khadījah, Jibrīl conveys to you the greeting of peace.”
In some reports the wording is: “O Muḥammad, convey to Khadījah greetings of peace from her Lord.” (2)

From Ḥudhayfah: the Messenger of Allah ﷺ said, “Khadījah was the first of the women of all the worlds to believe in Allah and in Muḥammad ﷺ.” (3)
Its isnād is somewhat weak.

Ḥammād ibn Salamah, from Ḥumayd, from ʿAbd Allāh ibn ʿUbayd ibn ʿUmayr, said: “The Messenger of Allah ﷺ continued to mourn Khadījah so intensely that we feared for him, until he married ʿĀʾishah.” (4)

Maʿmar, from Qatādah; and Abū Jaʿfar al-Rāzī, from Thābit—the wording is that of Qatādah—from