Musnad Ahmad 1153:1640

Hammad ibn Usamah narrated to us, he said: Hisham informed us, from his father, from Aisha, who said: "I did not feel jealous of any woman as I felt jealous of Khadija, and she had perished three years before he married me, because of what I used to hear him mention of her. And his Lord, the Mighty and Majestic, had commanded him to give her glad tidings of a house of hollowed pearl in Paradise. And he would indeed slaughter a sheep, then gift portions of it to her female friends."