Narrated 'Aisha(R):Sahih Bukhari Volume 4, Book 55, Number 605:

"..The Prophet returned to Khadija while his heart was beating rapidly. She took him to Waraqa bin Naufal who was a Christian convert and used to read the Gospel in Arabic Waraqa asked (the Prophet), "What do you see?" When he told him, Waraqa said, "That is the same angel whom Allah sent to the Prophet) Moses. Should I live till you receive the Divine Message, I will support you strongly."

The other hadîth is:


Narrated 'Aisha(R)Sahih Bukhari: Volume 1, Book 1, Number 3

Khadija then accompanied him to her cousin Waraqa bin Naufal bin Asad bin 'Abdul 'Uzza, who, during the pre-Islamic Period became a Christian and used to write the writing with Hebrew letters. He would write from the Gospel in Hebrew as much as Allah wished him to write. He was an old man and had lost his eyesight. Khadija said to Waraqa, "Listen to the story of your nephew, O my cousin!" Waraqa asked, "O my nephew! What have you seen?" Allah's Apostle described whatever he had seen. Waraqa said, "This is the same one who keeps the secrets (angel Gabriel) whom Allah had sent to Moses. I wish I were young and could live up to the time when your people would turn you out." Allah's Apostle asked, "Will they drive me out?" Waraqa replied in the affirmative and said, "Anyone (man) who came with something similar to what you have brought was treated with hostility; and if I should remain alive till the day when you will be turned out then I would support you strongly." But after a few days Waraqa died.