From Sahih Bukhari (Hadith 6004):
Narrated `Aisha:I never felt so jealous of any woman as I did of Khadija, though she had died three years before the Prophet married me, and that was because I heard him mentioning her too often, and because his Lord had ordered him to give her the glad tidings that she would have a palace in Paradise, made of Qasab and because he used to slaughter a sheep and distribute its meat among her friends
Reference: Bukhari 6004