Musnad Ahmad 775:12

Yahya ibn Sa'id narrated to us, from Isma'il—meaning Ibn Abi Khalid—he said: I said to 'Abdullah ibn Abi Awfa: "Did the Messenger of Allah, peace and blessings of Allah be upon him, give glad tidings to Khadijah?" He said: "Yes, he gave her glad tidings of a house of hollowed pearl, in which there is no clamor and no toil."