“…‘Its oil would almost shine forth, even though no fire had touched it’ (Qur’an 24:35). Allah sets this parable for His Prophet, meaning: his very appearance is almost enough to announce his prophethood, even before he recites any portion of the Quran. As Ibn Rawaha versified:
Had no clear signs accompanied him at all,
His very bearing would itself convey the news.

I say: The faith of Khadijah, of Abu Bakr, and of the other earliest believers came before the splitting of the moon, before his reports of the unseen, and before his formal challenge with the Quran. Yet it followed their hearing of the Quran itself, which in its own right is a sign that necessarily proves his truthfulness. His mere words and his proclamation, “I am the Messenger of Allah,” together with what was already known of his character, likewise make his truthfulness inescapable, over and above the many other signs and proofs.
Indeed, Khadijah said to him: “Never! By Allah, Allah will never disgrace you. You uphold kinship ties, speak the truth, bear the burdens of others, and honor the guest…”