Hadithcore
Sahih Muslim, 2919 b
sahih

Jabir b. Samura reported:

I heard Allah's Messenger (ﷺ) as saying: There would lie open for a group of Muslims, or for a group of believers, the treasures of the family of Kisra which would be in the white (palace). In a version of Qutaiba there is definitely the word "Muslim".

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، وَأَبُو كَامِلٍ الْجَحْدَرِيُّ قَالاَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ سِمَاكِ، بْنِ حَرْبٍ عَنْ جَابِرِ بْنِ سَمُرَةَ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ ‏

‏ لَتَفْتَحَنَّ عِصَابَةٌ مِنَ الْمُسْلِمِينَ أَوْ مِنَ الْمُؤْمِنِينَ كَنْزَ آلِ كِسْرَى الَّذِي فِي الأَبْيَضِ ‏

‏ ‏.‏ قَالَ قُتَيْبَةُ مِنَ الْمُسْلِمِينَ ‏.‏ وَلَمْ يَشُكَّ ‏.‏

References2 variants
In-Book Reference
Book 54, Hadith 95
USC-MSA web (English) reference
Book 41, Hadith 6977 (deprecated numbering scheme)