Ibn Abbas explained the following Qur'anic verse: "O ye who believe! fasting is prescribed for you as it was prescribed for those before you" During the lifetime of the Prophet ﷺ, when the people offered night prayer, they were asked to abstain from food and drink and (intercourse with) women, they kept fast till the next night. A man betrayed himself and had intercourse with his wife after he had offered the night prayer, and he did not break his fast. So Allah, the Exalted, intended to make it (fasting) easy for those who survived, thus providing a concession and utility. Allah, the Glorified, said: "Allah knoweth what ye used to do secretly among yourselves." By this Allah benefited the people and provided concession and ease to them.  

عَنِ ابْنِ عَبَّاسٍ { يَا أَيُّهَا الَّذِينَ آمَنُوا كُتِبَ عَلَيْكُمُ الصِّيَامُ كَمَا كُتِبَ عَلَى الَّذِينَ مِنْ قَبْلِكُمْ } فَكَانَ النَّاسُ عَلَى عَهْدِ النَّبِيِّ ﷺ إِذَا صَلَّوُا الْعَتَمَةَ حَرُمَ عَلَيْهِمُ الطَّعَامُ وَالشَّرَابُ وَالنِّسَاءُ وَصَامُوا إِلَى الْقَابِلَةِ فَاخْتَانَ رَجُلٌ نَفْسَهُ فَجَامَعَ امْرَأَتَهُ وَقَدْ صَلَّى الْعِشَاءَ وَلَمْ يُفْطِرْ فَأَرَادَ اللَّهُ ﷻ أَنْ يَجْعَلَ ذَلِكَ يُسْرًا لِمَنْ بَقِيَ وَرُخْصَةً وَمَنْفَعَةً فَقَالَ سُبْحَانَهُ { عَلِمَ اللَّهُ أَنَّكُمْ كُنْتُمْ تَخْتَانُونَ أَنْفُسَكُمْ } وَكَانَ هَذَا مِمَّا نَفَعَ اللَّهُ بِهِ النَّاسَ وَرَخَّصَ لَهُمْ وَيَسَّرَ  

Al Bara’ (bin Azib) said “When a man fasted and slept, he could not eat till (another nigh) like it.” Sarmah bin Qais Al Ansari came to his wife while he was fasting and asked her Do you have something (to eat)? She replied “No”. Let me go and seek something for you. So, she went out and sleep overcame him. She came (back) and said (to him) .You are deprived (of food). He fainted before noon. He used to work all day long at his land. This was mentioned to the Prophet ﷺ. So the following verse was revealed. “Permitted to you on the nights of the fasts, is the approach to your wives. They are your garments and ye are their garments. Allah knoweth what yes used to do secretly amongst yourselves. But he turned to you and forgave you. So now associate with them and seek what Allaah hath ordained for you. And eat and drink until the white thread of dawn appears to you. He recited up to the words “of dawn”.  

لاَ لَعَلِّي أَذْهَبُ فَأَطْلُبُ لَكَ شَيْئًا فَذَهَبَتْ وَغَلَبَتْهُ عَيْنُهُ فَجَاءَتْ فَقَالَتْ خَيْبَةً لَكَ فَلَمْ يَنْتَصِفِ النَّهَارُ حَتَّى غُشِيَ عَلَيْهِ وَكَانَ يَعْمَلُ يَوْمَهُ فِي أَرْضِهِ فَذَكَرَ ذَلِكَ لِلنَّبِيِّ ﷺ فَنَزَلَتْ { أُحِلَّ لَكُمْ لَيْلَةَ الصِّيَامِ الرَّفَثُ إِلَى نِسَائِكُمْ } قَرَأَ إِلَى قَوْلِهِ { مِنَ الْفَجْرِ }