Subject: making love after sunset during Ramadan. I have committed a sin according to some friends by having made love with my spouse after the sunset during the Ramadan. They referred me to authentic Hadith and also scholars' Fatawa that this act is not allowed. It was beyond our knowledge of this act. Hence we are applying to you for an advise of what to do and what the Kaffarah is for this? If this is allowed, should one then make Wudu before eating the Suhur or is Wudu only obliged on performing Salah?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

If the matter is as you mentioned here, that you enjoyed sex with your wife after the sunset then there is no harm since Allah made lawful for a fasting person eating, drinking, having sex, etc. from sunset till dawn.  Allah Says (interpretation of meaning): {…So now have sexual relations with them and seek that which Allâh has ordained for you (offspring), and eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night), ….}[2:187].

However, if one has sex with his wife or he enters the state of major impurity he has to take a ritual bath before performing prayers.  No prayer is valid without taking a bath.  Delaying a prayer from its fixed time is forbidden.  Mere Wudu does not remove the major state of Janabah; one has to wash all his/her body with the intention of removing this impurity. 

However, to eat or drink Suhoor (the meal a fasting person takes before Fajr) one does not need Wudu or Ghusl.

Allah knows best.