From Sahih Bukhari (Hadith 3817):
Narrated `Aisha:I did not feel jealous of any woman as much as I did of Khadija because Allah's Messenger (ﷺ) used to mention her very often. He married me after three years of her death, and his Lord (or Gabriel) ordered him to give her the good news of having a palace of Qasab in Paradise
Reference: Bukhari 3817