Sunan an-Nasa'i, Hadith 1808 ⓘ
It was narrated that Umm Habibah said: "The Messenger of Allah said: 'Whoever prays twelve rak'ahs in a day apart from the obligatory prayers, Allah (SWT) will build for him, or there will be built for him, a house in Paradise.'"
أَخْبَرَنَا يَحْيَى بْنُ حَبِيبٍ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ عَاصِمٍ، عَنْ أَبِي صَالِحٍ، عَنْ أُمِّ حَبِيبَةَ، قَالَتْ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ صَلَّى فِي يَوْمٍ ثِنْتَىْ عَشْرَةَ رَكْعَةً سِوَى الْفَرِيضَةِ بَنَى اللَّهُ لَهُ أَوْ بُنِيَ لَهُ بَيْتٌ فِي الْجَنَّةِ " .
also referenced under: Book 20, Hadith 211 (In-Book) & Volume 2, Book 20, Hadith 1809 (DarusSalam)