Sahih Muslim Book 31, Hadith Number 5974.

Chapter : The merits of Hadrat Khadija, mother of the faithful (Allah be pleased with her).

‘Aisha reported: Never did I feel jealous of any wife amongst the wives of Allah’s Apostle (may peace be upon him) as I feel in case of Khadija (though I had never seen her), for he praised her very often.