Bara bin Azib reported,

The companions of Muhammad ﷺ used to follow this practice: if a man was fasting and the time of breaking the fast came, but he fell asleep before eating, he would not eat that night or the following day until evening came again.A certain man from the Ansar was fasting. When the time to break his fast arrived, he came to his wife and asked, "Do you have any food?"She replied, "No, but let me go and look for some for you."Sleep overcame him, and when his wife returned and saw him asleep, she said, "What a disappointment for you."By midday the next day, he had fainted from exhaustion. This was mentioned to the Prophet ﷺ, and so this verse was revealed, "It has been made permissible for you on the night of fasting to have intimate relations with your wives," up to His saying, "until the white thread of dawn becomes distinct to you from the black thread of night" [Baqarah 2:187].Abu Ahmad said that the man was Qays bin Sirmah al-Ansari, who came home and fell asleep, and he then mentioned the rest of the account.

حدثنا أسود بن عامر وأبو أحمد قالا حدثنا إسرائيل عن أبي إسحاق

عن البراء قال

كان أصحاب محمد ﷺ إذا كان الرجل صائما فحضر الإفطار فنام قبل أن يفطر لم يأكل ليلته ولا يومه حتى يمسي وإن فلانا الأنصاري كان صائما فلما حضره الإفطار أتى امرأته فقال هل عندك من طعام قالت لا ولكن أنطلق فأطلب لك فغلبته عينه وجاءت امرأته فلما رأته قالت خيبة لك فأصبح فلما انتصف النهار غشي عليه فذكر ذلك للنبي ﷺ فنزلت هذه الآية {أحل لكم ليلة الصيام الرفث إلى نسائكم} إلى قوله {حتى يتبين لكم الخيط الأبيض من الخيط الأسود} قال أبو أحمد وإن قيس بن صرمة الأنصاري جاء فنام فذكره