It is made lawful for you to have sexual relation with your wives on the night of As-Saum (the fasts) ... (till) ... and seek that which Allah has ordained for you (offspring).. . (V.2:187)

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)