When the order of compulsory fasting of Ramadan was revealed, the people did not have sexual relations with their wives for the whole month of Ramadan, but some men cheated themselves (by violating that restriction). So Allah revealed: "Allah is aware that you were deceiving yourselves but He accepted your repentance and forgave you.." (3.187)
سَمِعْتُ الْبَرَاءَ ؓ لَمَّا نَزَلَ صَوْمُ رَمَضَانَ كَانُوا لاَ يَقْرَبُونَ النِّسَاءَ رَمَضَانَ كُلَّهُ وَكَانَ رِجَالٌ يَخُونُونَ أَنْفُسَهُمْ فَأَنْزَلَ اللَّهُ {عَلِمَ اللَّهُ أَنَّكُمْ كُنْتُمْ تَخْتَانُونَ أَنْفُسَكُمْ فَتَابَ عَلَيْكُمْ وَعَفَا عَنْكُمْ}