Abdullah bin Abbas reported,
"You who believe, fasting has been prescribed for you as it was prescribed for those before you" [Baqarah 2:183].In the time of the Messenger of Allah ﷺ, once the people had performed the evening prayer, food, drink, and intimacy with women became forbidden to them, and they would fast until the following night. Then a man betrayed himself and had relations with his wife after he had prayed the evening prayer, without having broken his fast. So Allah 
willed to make this an ease for those who remained, a concession and a benefit, and the Exalted said, "Allah knows that you have been deceiving yourselves" [Baqarah 2:187]. This was among the matters by which Allah brought benefit to people, granting them concession and ease.
Azami 11959
Hasanعن ابن عباس
{يأيها الذين ءامنوا كتب عليكم الصيام كما كتب على الذين من قبلكم} فكان الناس على عهد رسول الله ﷺ إذا صلوا العتمة حرم عليهم الطعام والشراب والنساء، وصاموا إلى القابلة فاختان رجل نفسه، فجامع امرأته وقد صلى العشاء، ولم يفطر فأراد الله عز وجل أن يجعل ذلك يسرا لمن بقي، ورخصة ومنفعة، فقال سبحانه: {علم الله أنكم كنتم تختانون أنفسكم} وكان هذا مما نفع الله به الناس، ورخص لهم ويسر.
Abu Dawud (2313) narrated it from Ahmad bin Muhammad bin Shabuya, who said, Ali bin Husayn bin Waqid told me, from his father, from Yazid Nahwi, from Ikrima, from Ibn Abbas, and he related it.Its isnad is hasan because of Ali bin Husayn bin Waqid and his father, for the two of them make the hadith hasan.