Sahih Muslim , Book 53, Hadith 49 (In-Book) ⓘ
Anas reported Allah's Apostle as saying: There would be left some space in Paradise as Allah would like that to be left. Then Allah would create another creation as He would like.
حَدَّثَنِي زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا عَفَّانُ، حَدَّثَنَا حَمَّادٌ، - يَعْنِي ابْنَ سَلَمَةَ - أَخْبَرَنَا ثَابِتٌ، قَالَ سَمِعْتُ أَنسًا، يَقُولُ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " يَبْقَى مِنَ الْجَنَّةِ مَا شَاءَ اللَّهُ أَنْ يَبْقَى ثُمَّ يُنْشِئُ اللَّهُ تَعَالَى لَهَا خَلْقًا مِمَّا يَشَاءُ " .
also referenced under: Hadith 2848 (Reference) & Book 40, Hadith 6826 (USC-MSA)