It is narrated from Sayyiduna Ka'b bin Malik (may Allah be pleased with him) that in the beginning of Ramadan, when a fasting person slept at night, eating, drinking, and approaching one's wife would become forbidden for him until he broke his fast the next day. Once, Sayyiduna Umar spent some time at night with the Prophet (peace and blessings be upon him) and then returned home to find his wife sleeping. He intended to fulfill his desire with her, so she said, "I had fallen asleep." Sayyiduna Umar said, "Where had you slept?" Then he fulfilled his desire with her. The same happened with Sayyiduna Ka'b bin Malik (may Allah be pleased with him). The next day, when Sayyiduna Umar informed the Prophet (peace and blessings be upon him) of this incident, Allah revealed this verse: "Allah knows that you were betraying yourselves, so He turned to you and forgave you."