Did sexual intercourse occur between the Messenger of Allah, peace and blessings be upon him, and Khadijah, may Allah be pleased with her, before marriage?

Khadijah was a wealthy and intelligent businesswoman. She hired the Prophet, peace and blessings be upon him, before his prophethood, to work in her trade. Her trade prospered, and when the Prophet, peace and blessings be upon him, returned, Mayṣarah, her servant, informed her about the signs he had witnessed indicating his prophethood. Khadijah was impressed by him and proposed to him. This confirms that the Prophet, peace and blessings be upon him, is infallible from anything that could compromise his modesty or contradict chivalry, and that all prophets are the most perfect and best of humanity. They are infallible from major and minor sins that could diminish their status.

And whoever slanders a prophet has committed disbelief and deserves to be killed.