سنن ابن ماجه

It was narrated that ‘Asim bin ‘Amr said: “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 (ﷺ) and he said: “As for a man’s prayer in his house, it is light, so illuminate your houses.’”” Another chain with similar wording.