Sunan Ibn Majah, Chapter: The Chapters of Establishing the Prayer and the Sunnah Regarding Them

"A group from the people of 'Iraq came to Umar and when they came to him, he said to them: 'Where are you from?' They said: 'From the inhabitants of 'Iraq.' He said: 'Have you come with permission?' They said: 'Yes.' Then they asked him about a man's prayer in his house. Umar said: 'I asked the Messenger of Allah (saw) and he said: "As for a man's prayer in his house, it is light, so illuminate your houses.'"" Daif