Allah ta^ala said: The ayah
(وَلَئِن سَأَلْتَهُمْ لَيَقُولُنَّ إِنَّمَا كُنَّا نَخُوضُ وَنَلْعَبُ قُلْ أَبِاللهِ وَءايَاتِهِ وَرَسُولِهِ كُنتُمْ تَسْتَهْزِؤُونَ)
that means: If they [the kuffar] were questioned they would say we were just talking and joking. Say to them: Is it Allah, his ayat and messenger you were belittling!! Do not give any excuse. You committed kufr after you had the belief (at-Tawbah 65-66).