Question: A man slept beside his wife after eating Suhoor (pre-dawn meal before the Fast) in Ramadaan and he was confused concerning the loud recitation of the Imaam (leader in congregational Prayer) in the mosque. He thought that it was Tahajjud (optional late night Prayer) and did not try to find out whether it was the Fajr (Dawn) Prayer or the Tahajjud Prayer, and he finally copulated with his wife. Surely, this man was able to turn on the light to know the time but he did not. However, after he had sex, he found out that it was the Fajr Prayer. By doing so, is he regarded as careless with and degrading the prohibitions of Allaah?
Answer: If the reality is as mentioned, that he had sexual intercourse with his wife after the break of Fajr in Ramadaan, thinking that the night did not elapse, he is not sinful because he did not seek to have sexual intercourse in the daytime in Ramadaan… read more here.