The Prophet ﷺ said, "Whoever recites Say, He is Allah, the One ten times to its completion, Allah will build for him a palace in Paradise."Umar bin Khattab said, "In that case, Messenger of Allah, we will recite it abundantly."The Messenger of Allah ﷺ replied, "Allah has more and better to give."
حدثنا حسن حدثنا ابن لهيعة قال وحدثنا يحيى بن غيلان حدثنا رشدين حدثنا زبان بن فائد الحبراني عن سهل بن معاذ بن أنس الجهني
عن النبي ﷺ قال من قرأ قل هو الله أحد حتى يختمها عشر مرات بنى الله له قصرا في الجنة فقال عمر بن الخطاب إذن أستكثر يا رسول الله فقال رسول الله ﷺ الله أكثر وأطيب
Its isnad is daif because of Rushdin, but Hakim graded the hadith of Zaban and Rushdin sahih, and Dhahabi agreed with him, as in the following hadith. The hadith was narrated by Darimi 2/551, no. 3429, in the Virtues of the Quran, the virtue of "Say, He is Allah, the One", and by Ibn Sunni in Amal al-Yawm, 221, no. 687.