Sayyiduna Abdullah bin al-Harith (may Allah be pleased with him) says that Sayyiduna Ammar bin Yasir (may Allah be pleased with him) mentioned the story of the marriage of Sayyidah Khadijah (may Allah be pleased with her): that Sayyidah Khadijah (may Allah be pleased with her) spoke to her brother, and he spoke to their father, who had been given wine to drink. He mentioned the Messenger of Allah (peace and blessings be upon him) and his standing, and asked about the marriage of Sayyidah Khadijah (may Allah be pleased with her), so he married Sayyidah Khadijah (may Allah be pleased with her) (to him). Then he slept and woke up sober, and denied having married Sayyidah Khadijah (to him). He said: Where is that companion of yours whom you claim I have married her to? When the Prophet (peace and blessings be upon him) came forward and he looked at him, he said: If I have married her (to him), then so be it; and if I have not, then I now marry her (to him).
(b) Imam al-Zuhri (may Allah have mercy on him) says that the Prophet (peace and blessings be upon him) married Sayyidah Khadijah (may Allah be pleased with her) in the time of ignorance (Jahiliyyah), and her father Khuwaylid bin Asad conducted her marriage.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13747