Sahih Muslim · Hadith 7359
The Book Pertaining to Paradise; Its Description; Its Bounties and Its Intimates - كتاب الجنة وصفة نعيمها وأهلها
حدثني زهير بن حرب، حدثنا عفان، حدثنا حماد، - يعني ابن سلمة - أخبرنا ثابت، قال سمعت أنسا، يقول عن النبي صلى الله عليه وسلم قال " يبقى من الجنة ما شاء الله أن يبقى ثم ينشئ الله تعالى لها خلقا مما يشاء " .
Anas reported Allah's Apostle (may peace be upon him) 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.
Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).