The Prophet ﷺ said, "Whoever recites 'Say, He is Allah, the One' [Ikhlas 112:1] ten times to its completion, Allah will build for him a palace in Paradise."Umar bin Khattab said, "Then I shall recite it abundantly, Messenger of Allah."The Messenger of Allah ﷺ replied, "Allah has more to give, and what He gives is purer."
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.
Ahmad narrated it (15610), saying, Hasan told us, Ibn Lahia told us, he said, and Yahya bin Ghaylan told us, Rushdin told us, both of them said, Zabban bin Fayd Hamrawi told us, from Sahl bin Muaz bin Anas Juhani, from his father Muaz bin Anas Juhani, who said, and he mentioned it.Ibn Lahia has been criticized, but he has a corroborating narrator, Rushdin bin Saad corroborated him as shown in the chain. Their shared teacher, Zabban bin Fayd Basri Hamrawi, is disputed. Ahmad bin Hanbal said of him, "His hadiths are objectionable (munkar)." Ibn Main said, "A weak (daif) sheikh." Abu Hatim said, "Sound (salih)."This is strengthened by the mursal report of Saeed bin Musayab, narrated by Darimi (3472) from Abdullah bin Yazid, who said, Haywa told us, Abu Aqeel (whose name is Zahra bin Mabad) told me that he heard Saeed bin Musayab say, the Prophet ﷺ said, "Whoever recites Say, He is Allah, One eleven times will have a palace built for him in Paradise because of it. Whoever recites it twenty times will have two palaces built for him because of it. And whoever recites it thirty times will have three palaces built for him because of it."Umar bin Khattab said, "By Allah, Messenger of Allah, at this rate our palaces will multiply greatly!" The Messenger of Allah ﷺ said, "Allah is more generous than that."Through these two chains, the hadith rises to the level of hasan, except for its statement, "Whoever recites it twenty times will have two palaces built for him, and whoever recites it thirty times will have three palaces built for him." Perhaps one of the narrators calculated this based on the reward for ten recitations and rendered it as part of the raised (marfu) wording.