Sahih Bukhari Volume 7, Book 62, Hadith Number 156.

Narrated By ‘Aisha : I never felt so jealous of any wife of Allah’s Apostle as I did of Khadija because Allah’s Apostle used to remember and praise her too often and because it was revealed to Allah’s Apostle that he should give her (Khadija) the glad tidings of her having a palace of Qasab in Paradise.