The Book of the Merits of the Companions
حَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدَةُ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، قَالَتْ بَشَّرَ رَسُولُ اللَّهِ صلى الله عليه وسلم خَدِيجَةَ بِنْتَ خُوَيْلِدٍ بِبَيْتٍ فِي الْجَنَّةِ .A'isha reported that Allah's Messenger (may peace he upon him) gave glad tidings to Khadija bint Khuwailid of a palace in Paradise
From Sahih Muslim, whose reports the scholars accept as authentic.