Sahih Bukhari Volume 5, Book 58, Hadith Number 166.

Narated By ‘Aisha : I did not feel jealous of any of the wives of the Prophet as much as I did of Khadija though I did not see her, but the Prophet used to mention her very often, and when ever he slaughtered a sheep, he would cut its parts and send them to the women friends of Khadija. When I sometimes said to him, “(You treat Khadija in such a way) as if there is no woman on earth except Khadija,” he would say, “Khadija was such-and-such, and from her I had children.”